Gems have refractive index, dispersion,
specific gravity, hardness, cleavage, fracture, and lustre. They may
exhibit pleochroism or double refraction. They may have luminescence
and a distinctive absorption spectrum.
Material or flaws within a stone
may be present as inclusions. The gem may occur in certain locations,
called the "occurrence".
Value
A gemstone is prized especially for
great beauty or perfection so appearance is almost always the most
important attribute of gemstones. Characteristics that make a stone
beautiful or desirable are colour, unusual optical phenomena within
the stone, an interesting inclusion such as a fossil, rarity, and
sometimes the form of the natural crystal. Diamond is prized highly
as a gemstone since it is the hardest naturally occurring substance
known and is able to reflect light with fire and sparkle when faceted.
However, diamonds are far from rare with millions of carats mined
each year.
Traditionally, common gemstones were
classified into precious stones (cardinal gems) and semi-precious
stones. The former category was largely determined by a history of
ecclesiastical, devotional or ceremonial use and rarity. Only five
types of gemstones were considered precious: diamond, ruby, sapphire,
emerald, and amethyst. In current usage by gemologists, all gems are
considered precious, although four of the five original "cardinal
gems" (excluding the now-common amethyst) are usually -- but
not always -- the most valuable.
Rare or unusual gemstones, generally
meant to include those gemstones which occur so infrequently in gem
quality that they are scarcely known except to connoisseurs, include
andalusite, axinite, cassiterite, clinohumite and iolite.
A selection of gemstone pebbles made
by tumbling rough rock with abrasive grit, in a rotating drum. The
biggest pebble here is 40 mm long (1.6 inches).
Factors influencing the esteem in
which gems are held are attractiveness, durability, rarity, fashion,
and size.
Treatments applied to gemstones
Gemstones are often treated to enhance
the color or clarity of the stone. Depending on the type and extent
of treatment, they can affect the value of the stone. Some treatments
are used widely and accepted in practice while others are not accepted.
Heat
When heated, yellow and white topaz
turn differing shades of pink.
Radiation
Most blue topaz, especially the darker
blues such as "London" blue, has been irradiated to change
the color from white to blue.
Waxing
/ Oiling
Emeralds contain natural fissures
that are sometimes filled with wax or oil to disguise them. This wax
or oil is also colored to make the emerald appear of better color
as well as clarity.
Coatings
More recently, some gemstones have
been enhanced with a coating that changes the color and appearance
of the gem. For instance, topaz is sometimes treated with a layer
of titanium dioxide that changes the color to golden with some iridescence.
This coating is not permanent and can be damaged by scratching.
Synthetic and artificial
gemstones
Some gemstones are manufactured to
imitate other gemstones. For example, cubic zirconia is a synthetic
diamond simulant composed of zirconium oxide. The imitations copy
the look and colour of the real stone but possess neither their chemical
nor physical characteristics. However, true synthetic gemstones are
not necessarily imitation. For example, diamonds, ruby, sapphires
and emeralds have been manufactured in labs, which possess very nearly
identical chemical and physical characteristics to the genuine article.
Synthetic corundums, including ruby and sapphire, are very common
and they cost only a fraction of the natural stones. Smaller synthetic
diamonds have been manufactured in large quantities as industrial
abrasives for many years. Only recently, larger synthetic diamonds
of gemstone quality, especially of the coloured variety, have been
manufactured.
Gemstones
There are over 130 species of minerals that have been cut into gems
with 50 species in common use. These include:
Agate, Alexandrite and other varieties of chrysoberyl, Amethyst (originally
a "cardinal gem", but now no longer so, since huge quantities
were discovered in Brazil and the price plummeted) Aquamarine and
other varieties of beryl Chrysocolla,Chrysoprase, Diamond, Emerald,
Feldspar (moonstone), Garnet, Hematite, Jade nephrite Jasper, Kunzite,
Lapis lazuli, Malachite, Obsidian, Olivine (Peridot), Opal(Girasol),
Pyrite, Quartz, Jasper and its varieties, such as tiger's-eye,
citrine, agate, and amethyst, Ruby, Sapphire, Spinel, Sugilite, Tanzanite
and other varieties of zoisite, Topaz, Turquoise, Tourmaline, Zircon.
Gem quality forming
Andalusite, Axinite, Benitoite, Bixbite
(Red beryl), Cassiterite, Clinohumite, Iolite, Kornerupine, Natural
moissanite, Zeolite (Thomsonite).
.
Artificial or synthetic, materials used as gems include:
High-lead glass, Synthetic cubic zirconia, Synthetic corundum, Synthetic
spinel, Synthetic
moissanite.
There are a number of organic materials
used as gems, including:
Amber, Bone, Coral, Ivory, Jet (lignite), Mother of pearl, Ammolite
- from fossils formed from the shells of extinct ammonites Pearl.
Agate
Agate is a term applied not to a
distinct mineral species, but to an aggregate of various forms of
silica, chiefly chalcedony. According to Theophrastus, the agate
(achates) was named from the river Achates, now the Drillo, in Sicily,
where the stone was first found.
Chemical formula Silica, SiO2.
Color: White to grey, light blue, orange to red, black.
Formation and characteristics
Most agates occur as nodules in volcanic
rocks or ancient lavas where they represent cavities originally produced
by the disengagement of volatiles in the molten mass which were then
filled, wholly or partially, by siliceous matter deposited in regular
layers upon the walls. Such agates, when cut transversely, exhibit
a succession of parallel lines, often of extreme tenuity, giving a
banded appearance to the section. Such stones are known as banded
agate, riband agate and striped agate.
In the formation of an ordinary agate,
it is probable that waters containing silica in solution -- derived,
perhaps, from the decomposition of some of the silicates in the lava
itself -- percolated through the rock and deposited a siliceous coating
on the interior of the vapour-vesicles. Variations in the character
of the solution or in the conditions of deposit may cause corresponding
variation in the successive layers, so that bands of chalcedony often
alternate with layers of crystalline quartz. Several vapour-vesicles
may unite while the rock is viscous, and thus form a large cavity
which may become the home of an agate of exceptional size; thus a
Brazilian geode lined with amethyst and weighing 35 tons was exhibited
at the Dusseldorf Exhibition of 1902.
The first deposit on the wall of
a cavity, forming the "skin" of the agate, is generally
a dark greenish mineral substance, like celadonite, delessite or "green
earth," which are rich in iron probably derived from the decomposition
of the augite in the enclosing volcanic rock. This green silicate
may give rise by alteration to a brown iron oxide (limonite), producing
a rusty appearance on the outside of the agate-nodule. The outer surface
of an agate, freed from its matrix, is often pitted and rough, apparently
in consequence of the removal of the original coating. The first layer
spread over the wall of the cavity has been called the "priming",
and upon this base zeolitic minerals may be deposited.
Many agates are hollow, since deposition
has not proceeded far enough to fill the cavity, and in such cases
the last deposit commonly consists of quartz, often amethyst, having
the apices of the crystals directed towards the free space so as to
form a crystal-lined cavity, or geode.
On the disintegration of the matrix
in which the agates are embedded, they are set free. The agates are
extremely resistant to weathering and remain as nodules in the soil
or are deposited as gravel in streams and shorelines.
Types
of agate
A Mexican agate, showing only a single
eye, has received the name of "cyclops agate." Included
matter of a green, golden, red, black or other colour or combinations
embedded in the chalcedony and disposed in filaments and other forms
suggestive of vegetable growth, gives rise to dendritic or moss agate
(named varieties include Maury Mountain, Richardson Ranch, Sheep Creek
and others). Dendritic agates have beautiful fern like patterns on
them formed due to the presence of manganese and iron ions. Other
types of included matter deposited during agate-building include sagenitic
growths (radial mineral crystals) and chunks of entrapped detritus
(such as sand, ash, or mud). Occasionally agate fills a void left
by decomposed vegetative material such as a tree limb or root and
is called limb cast agate due to its appearance.
A Turritella agate is formed from
fossil Turritella shells silicified in a chalcedony base. Turritella
are spiral marine gastropods having elongated, spiral shells composed
of many whorls. Similarly, coral, petrified wood and other organic
remains or porous rocks can also become agatized. Agatized coral is
often referred to as Petoskey agate or stone.
Certain stones, when examined in
thin sections by transmitted light, show a diffraction spectrum due
to the extreme delicacy of the successive bands, whence they are termed
rainbow agates. Often agate coexists with layers or masses of opal,
jasper or crystalline quartz due to ambient variations during the
formation process.
Other forms of agate include carnelian
agate (usually exhibiting reddish hues), Botswana agate, blue lace
agate, plume agate (such as Carey, Graveyard Point, Sage, St. Johns,
Teeter Ranch and others), tube agate (with visible flow channels),
fortification agate (which exhibit little or no layered structure),
fire agate (which seems glow internally like an opal) and Mexican
crazy-lace agate (which exhibits an often brightly colored, complex
banded pattern).
Agate beliefs
In Islam, agates are deemed to be
very precious stones. According to tradition, the wearer of an agate
ring, for example, is believed to be protected from various mishaps
and will enjoy longevity, among other benefits. In other traditions
agate is believed to cure the stings of scorpions and the bites of
snakes, soothe the mind, prevent contagion, still thunder and lightning,
promote eloquence, secure the favour of the powerful, and bring victory
over enemies. Persian magicians are also known to have prized agate
rings in their work and beliefs.
Uses in industry
Industry uses agates chiefly to make
ornaments such as pins, brooches, paper knives, inkstands, and seals.
Because of its hardness and ability to resist acids, agate is used
to make mortars and pestles to crush and mix chemicals.
Chrysoberyl
The mineral or gemstone chrysoberyl, not to be confused with beryl,
is an aluminate of beryllium with the formula BeAl2O4. Chrysoberyl
is transparent to transluc // if (window.showTocToggle) { var tocShowText
= "show"; var tocHideText = "hide"; showTocToggle();
} // ent and sometimes chatoyant. An interesting feature of uncut
crystals of chyrsoberyl is the cyclic twins called trillings.
These twinned crystals have a hexagonal appearance, but are the result
of a triplet of twins with each "twin" taking up 120 degrees
of the cyclic trilling. The word chrysoberyl is derived from
the Greek chrysos, "golden", and beryllos,
of uncertain etymology.
Occurrence
Chrysoberyl occurs in granitic rocks,
pegmatites and mica schists; often it is found in alluvial deposits.
It has also been found in contact metamorphic deposits of dolomitic
marble with corundum, and in fluorine bearing skarns. Most chrysoberyl
is recovered from river sands and gravels.
Chemical formula (or Composition):
Beryllium aluminium oxide, BeAl2O4.
Color: Various shades of green and yellow; brownish, reddish.
Major varieties: Alexandrite, Cymophane.
Alexandrite
variety
The alexandrite variety displays
a color change (alexandrite effect) dependent upon light,
along with strong pleochroism. Alexandrite results from small scale
replacement of aluminium by chromium oxide, which is responsible for
alexandrite's characteristic green to red color change. Alexandrite
from the Ural Mountains in Russia is green by daylight and red by
incandescent light. Other varieties of alexandrite may be yellowish
or pink in daylight and a columbine or raspberry red by incandescent
light. The optimum or "ideal" color change would be fine
emerald green to fine purplish red, but this is exceedingly rare.
Because of their rarity and the color change capability, "ideal"
alexandrite gems are some of the most expensive in the world.
Alexandrite was first discovered
in 1831 in an emerald mining region of the Ural Mountains in Russia.
The name comes from Tsar Alexander II of Russia, on whose birthday
the gem was discovered in that country. It was named "alexandrite"
in his honor by the mineralogist Adolf Erik Nordenskiöld. It
is an interesting coincidence that the Russian national colors are
green and red, which may have originated from this gem.
The finest alexandrites were found
in the Ural Mountains, the largest cut stones being in the 30 carat
(6 g) range, though many fine examples have been discovered in Sri
Lanka (up to 65 cts.), India (Andhra Pradesh), Brazil, Myanmar, and
especially Zimbabwe (small stones usually under 1 carat (200 mg) but
with intense color change). Overall, stones from any locale over 5
carats (1 g) would be considered extremely rare, especially gems with
fine color change. Alexandrite is both hard and tough, making it very
well suited to wear in jewelry.
The gem has given rise to the adjective
"alexandritic", meaning any transparent gem or material
which shows a noted change in color between natural and incandescent
light. Some other gem varieties of which alexandritic specimens have
been found include sapphire, garnet, and spinel.
Some gemstones described as lab-grown
(synthetic) alexandrite are actually corundum laced with trace elements
(e.g., vanadium) or color-change spinel and are not actually chrysoberyl.
As a result, they would be more accurately described as simulated
alexandrite rather than synthetic.
Synthetic alexandrite is used as
an active laser medium. Alexandrite laser crystals tend to be round,
with a pale brown tint.
Cymophane
variety
A chrysoberyl gemstone featuring a somewhat asymmetric, "native"
oval mixed cut.Translucent yellowish chatoyant chyroberyl is called
cymophane or cat's eye. Cymophane has its derivation also
from the Greek words meaning wave and appearance, in reference to
the chatoyancy sometimes exhibited. In this variety, microscopic tubelike
cavities or needlelike inclusions of rutile occur in an orientation
parallel to the c-axis producing a chatoyant effect visible as a single
ray of light passing across the crystal. This effect is best seen
in gemstones cut in cabochon form perpendicular to the c-axis. The
color in yellow chrysoberyl is due to Fe3+ impurities.
Although other minerals such as tourmaline,
scapolite, corundum, spinel and quartz can form "cat's eye"
stones similar in appearance to cymophane, the jewelry industry designates
these stones as "quartz cat's eyes", or "ruby cat's
eyes" and only chrysoberyl can be referred to as "cat's
eye" with no other designation.
Amethyst
Amethyst (SiO2) is a violet or purple variety of quartz often used
as an ornament. The name comes from the Greek a (not) and
methuskein ("to intoxicate"), a reference to the
belief that the stone protected its owner from drunkenness; the ancient
Greeks and Romans wore amethyst and made drinking vessels of it in
the belief that it would prevent intoxication.
Chemistry
In the 20th century, the color of
amethyst was attributed to the presence of manganese. However, since
it is capable of being greatly altered and even discharged by heat,
the color was believed by some authorities to be from an organic source.
Ferric thiocyanate was suggested, and sulfur was said to have been
detected in the mineral. On exposure to heat, amethyst generally becomes
yellow, and much of the citrine, cairngorm, or yellow quartz of jewelry
is said to be merely "burnt amethyst". Veins of amethystine
quartz are apt to lose their color on the exposed outcrop.
Composition
Amethyst is composed of an irregular
superposition of alternate lamellae of right-handed and left-handed
quartz. It has been shown that this structure may be due to mechanical
stresses. As a consequence of this composite formation, amethyst is
apt to break with a rippled fracture, or to show "thumb markings",
and the intersection of two sets of curved ripples may produce on
the fractured surface a pattern something like that of "engine
turning". Some mineralogists, following Sir David Brewster, apply
the name of amethyst to all quartz which exhibits this structure,
regardless of color.
Because it has a hardness of 7 on
the Mohs scale, amethyst is treasured for its use in jewelry. However,
it is still just 1/15 as hard as diamond.
History
Amethyst was used as a gemstone by
the ancient Egyptians and was largely employed in antiquity for intaglios.
Beads of amethyst are found in Anglo-Saxon graves in England. It is
a widely distributed mineral, but fine, clear specimens that are suitable
for cutting as ornamental stones are confined to comparatively few
localities. Such crystals occur either in the cavities of mineral-veins
and in granitic rocks, or as a lining in agate geodes. A huge geode,
or "amethyst-grotto", from near Santa Cruz in southern Brazil
was exhibited at the Düsseldorf Exhibition of 1902. Many of the
hollow agates of Brazil and Uruguay contain a crop of amethyst crystals
in the interior. Much fine amethyst comes from Russia, especially
from near Mursinka in the Ekaterinburg district, where it occurs in
drusy cavities in granitic rocks. Many localities in India yield amethyst;
and it is found also in Sri Lanka, chiefly as pebbles.
Alternate terminology
Due to its popularity as a gemstone,
several descriptive terms have been coined in the gem trade to describe
the varying colors of amethyst. "Rose de France" is usually
a pale pinkish lavender or lilac shade (usually the least sought color).
The most prized color is an intense violet with red flashes and is
called "Siberian", although gems of this color may occur
from several locations other than Siberia, notably Uruguay and Zambia.
In more recent times, certain gems (usually of Bolivian origin) that
have shown alternate bands of amethyst purple with citrine orange
have been given the name ametrine.
Purple corundum, or sapphire of amethystine
tint, is called Oriental amethyst, but this expression is often applied
by jewellers to fine examples of the ordinary amethystine quartz,
even when not derived from eastern sources. Professional gemological
associations, such as the Gemological Institute of America (GIA) or
the American Gemological Society (AGS), discourage the use of the
term "Oriental amethyst" to describe any gem, as it may
be misleading.
Geographic
distribution
Amethyst occurs at many localities
in the United States, but these specimens are rarely fine enough for
use in jewelry. Among these may be mentioned Amethyst Mountain, Texas;
Yellowstone National Park; Delaware County, Pennsylvania; Haywood
County, North Carolina; and Deer Hill, and Stow, Maine. It is found
also in the Lake Superior district. Amethyst is relatively common
in northwestern Ontario, but uncommon elsewhere in Canada; it was
selected as the provincial mineral of Ontario in 1975.
Value
Traditionally included in the cardinal,
or most valuable, gemstones (along with diamond, sapphire, ruby and
emerald), amethyst has lost much of its value due to the discovery
of extensive deposits in locations such as Brazil.
Amethyst
in folklore and astrology
Amethyst is the birthstone associated
with February. It is also associated with the Astrological signs of
Pisces, Aries (especially the violet and purple variety), Aquarius,
and Sagittarius. It is a symbol of heavenly understanding, and of
the pioneer in thought and action on the philosophical, religious,
spiritual and material planes. Ranking members of the Roman Catholic
Church traditionally wear rings set with a large amethyst as part
of their office.
The Greek word "amethystos"
basically can be translated as "not drunken." Amethyst was
considered to be a strong antidote against drunkenness, which is why
wine goblets were often carved from it. Supposedly, when a drunken
Dionysus was pursuing a maiden called Amethystos, who refused his
affections, she prayed to the gods to remain chaste. The goddesss
Artemis granted the prayer, transforming her into a white stone; humbled
by Amethystos' desire to remain chaste, Dionysus poured wine over
the stone she had become as an offering, dying the crystals purple.
The legend of the origin of amethyst
comes from Greek myths. Dionysius, the god of intoxication, was angered
one day by an insult from a mere mortal and swore revenge on the next
mortal that crossed his path, creating fierce tigers to carry out
his wish. Along came unsuspecting Amethyst, a beautiful young maiden
on her way to pay tribute to the goddess Diana. Diana turned Amethyst
into a stature of pure crystalline quartz to protect her from the
brutal claws. Dionysus wept tears
of wine in remorse for his action
at the sight of the beautiful statue. The god's tears stained the
quartz purple, creating the gem we know today".
Aquamarine
Aquamarine (Lat. aqua marina, "water of the sea")
is a gemstone-quality transparent variety of beryl, having a delicate
blue or turquoise color, suggestive of the tint of seawater. It's
closely related to the gem emerald. Colors vary and yellow beryl,
called heliodor; rose pink beryl, morganite; and
white beryl, goshenite are known.
Aquamarine is a beryl with a hexagonal
crystal structure and a chemical formula of Be3Al2Si6O18, a beryllium
aluminium silicate mineral. It has a specific gravity of 2.68 to 2.74
and a Mohs hardness of from 7.5 to 8. Aquamarine typically is on the
low end of the specific gravity range, normally at less than 2.7.
The pink variety exhibits a high specific gravity of around 2.8. Refractive
indices range around 1.57 to 1.58.
It occurs at most localities which
yield ordinary beryl, some of the finest coming from Russia. The gem-gravel
placer deposits of Sri Lanka contain aquamarine. Clear yellow beryl,
such as occurs in Brazil, is sometimes called aquamarine chrysolite.
When corundum presents the bluish tint of typical aquamarine, it is
often termed Oriental aquamarine.
In the United States, aquamarines
can be found at the summit of Mt. Antero in the Sawatch Range in central
Colorado. In Brazil, there are mines in the states of Minas Gerais,
Espírito Santo and Bahia. Zambia also produces nice aquamarine
as well as Madagascar, Malawi, Tanzania and Kenya. Much of today's
aquamarine is heated to give it a better color blue. The deeper the
blue color, the more valuable the gem is considered.
The biggest aquamarine ever mined
was found at the city of Marambaia, Minas Gerais, Brazil, in 1910.
It weighed over 110 kg, and its dimensions were 48.5 cm long and 42
cm in diameter.
Aquamarine is the official state
gem of Colorado.
Culture
and historical/mythical usage
Aquamarine is the birthstone associated
with March. It is also the gemstone for the 19th Anniversary.
People in the Middle Ages thought
that aquamarine could magically overcome the effects of poison.
Ancient sailors traveled with aquamarine
crystals, believing that it would ensure a safe passage, and often
slept with the stones under their pillow to ensure sound sleep. They
believed the siren’s (mermaid) fish-like lower body was made
of aquamarine.
Chrysocolla
Chrysocolla (hydrated copper silicate) is a mineral, CuSiO3·nH2O.
It is of secondary origin and forms in the oxidation zones of copper
ore bodies. Associated minerals are quartz, limonite, azurite, malachite,
cuprite, and other secondary copper minerals.
Chrysocolla is an attractive blue-green
colour and is minor ore of copper, having a hardness of 2.5 to 3.5.
It is also used as an ornamental stone. It is typically found as glassy
botryoidal or rounded masses and crusts, or vein fillings.
The name comes from the Greek chrysos,
"gold", and kolla, "glue", in allusion to the
name of the material used to solder gold, and was first used by Theophrastus
in 315 BCE.
Notable occurrences include Israel,
Democratic Republic of Congo, Chile, Cornwall in England, and Arizona,
Utah, New Mexico and Pennsylvania in the United States.
Quartz
Quartz is one of the most common minerals in the Earth's continental
crust. It belongs to the hexagonal crystal system, and is made up
of silicon, (SiO2), tetrahedra. Quartz has a hardness of 7 on the
Mohs scale. Density is 2.65 g/cm³. The typical shape is a six-sided
prism that ends in six-sided pyramids, although these are often twinned,
distorted, or so massive that only part of the shape is apparent from
a mined specimen. Additionally a bed is a common form, particularly
for varieties such as amethyst, where the crystals grow up from a
matrix and thus only one termination pyramid is present. A quartz
geode consists of a hollow rock (usually with an approximately spherical
shape) with a core lined with a bed of crystals.
Chemical formula (or Composition):
Silica (silicon dioxide, SiO2).
Color: Clear (if no impurities); also see Varieties.
Major varieties:
Chalcedony.
Any cryptocrystalline quartz, although
generally only used for white or lightly colored material.. Otherwise
more specific names are used.
Agate: Banded Chalcedony, translucent.
Onyx: Agate where the bands are straight, parallel and consistent
in size.
Jasper: Opaque chalcedony, impure.
Aventurine: Translucent chalcedony with small inclusions (usually
mica) that shimmer.
Tiger's eye: Fibrous quartz, exhibiting chatoyancy.
Rock Crystal: Clear, colorless.
Ruby Quartz: Crimson glass-like crystal, absorbs vast amounts of solar
energy.
Amethyst: Purple, transparent.
Citrine: Yellow to reddish orange, greenish yellow.
Prasiolite: Mint green, transparent.
Rose quartz: Pink, translucent, may display diasterism.
Milk quartz or snow quartz: White, translucent to opaque, may display
diasterism.
Smoky quartz: Brown, transparent.
Morion: Dark-brown, opaque.
Carnelian: Reddish orange
chalcedony, translucent.
Varieties
Quartz is one of the most common
minerals of the continental crust and goes by a bewildering array
of different names. The most important distinction between types of
quartz is that of macrocrystalline (individual crystals visible
to the unaided eye) and the microcrystalline or cryptocrystalline
varieties (aggregates of crystals visible only under high magnification).
Chalcedony is a generic term for cryptocrystalline quartz. The cryptocrystalline
varieties are either translucent or mostly opaque, while the transparent
varieties tend to be macrocrystalline.
Although many of the varietal names
historically arose from the colour of the mineral, current scientific
naming schemes refer primarily to the microstructure of the mineral.
Colour is a secondary identifier for the cryptocrystalline minerals,
although it is a primary identifier for the macrocrystalline varieties.
This does not always hold true.
Not all varieties of quartz are naturally
occurring. Prasiolite, an olive coloured material, is produced by
heat treatment; natural prasiolite has also been observed in Lower
Silesia in Poland. Although citrine occurs naturally, the majority
is the result of heat-treated amethyst. Carnelian is widely heat-treated
to deepen its color.
Milk
quartz
Because natural quartz is so often
twinned, much quartz used in industry is synthesized. Large, flawless
and untwinned crystals are produced in an autoclave via the hydrothermal
process: emeralds are also synthesized in this fashion.
Quartz occurs in hydrothermal veins
and pegmatites. Well-formed crystals may reach several metres in length
and weigh hundreds of kilograms. These veins may bear precious metals
such as gold or silver, and form the quartz ores sought in mining.
Erosion of pegmatites may reveal expansive pockets of crystals, known
as "cathedrals".
Quartz is a common constituent of
granite, sandstone, limestone, and many other igneous, sedimentary,
and metamorphic rocks.
Tridymite and cristobalite are high
temperature polymorphs of SiO2 which occur in high silica volcanic
rocks. Lechatelierite is an amorphous silica glass SiO2 which is formed
by lightning strikes in quartz sand.
History
The name "quartz" comes
from the German "Quarz", which is of Slavic origin (Czech
miners called it křem). Other sources insist the name is from
the Saxon word "Querkluftertz", meaning cross-vein ore.
Quartz is the most common material
identified as the mystical substance maban in Australian Aboriginal
mythology.
Roman naturalist Pliny the Elder believed quartz to be permanently
frozen ice. He supported this idea by saying that quartz is found
near glaciers in the Alps and that large quartz crystals were fashioned
into spheres to cool the hands. He also knew of the ability of quartz
to split light into a spectrum.
Nicolas Steno's study of quartz paved
the way for modern crystallography. He discovered that no matter how
distorted a quartz crystal, the long prism faces always made a perfect
60 degree angle.
Charles Sawyer invented the commercial
quartz crystal manufacturing process in Cleveland, OH. This initiated
the transition from mined and cut quartz for electrical appliances
to manufactured quartz.
The quartz oscillator or resonator
was first developed by Walter Guyton Cady in 1921 .George Washington
Pierce designed and patented quartz crystal oscillators in 1923 .
Warren Marrison created the first quartz oscillator clock based on
the work of Cady and Pierce in 1927.
Chrysoprase
Chrysoprase (also chrysophrase) is
a gemstone variety of chalcedony (fibrous form of quartz) that contains
small quantities of nickel. Its color is normally apple-green, but
varies to deep green. It is cryptocrystalline, which means that it
is composed of crystals so fine that they cannot be seen as distinct
particles under normal magnification. This sets it apart from rock
crystal, amethyst, citrine, and the other varieties of crystalline
quartz which are basically transparent and formed from easily recognized
six-sided crystals. Other members of the cryptocrystalline quartz
family include agate, carnelian, and onyx. Unlike many non-transparent
members of the quartz family, it is the color of chrysoprase, rather
than any pattern of markings, that makes it desirable. The word chrysoprase
comes from the Greek chrysos meaning 'gold' and prason,
meaning 'leek'.
Due to its comparative scarcity and
pleasing green color, chrysoprase is one of the most prized varieties
of quartz. Higher quality specimens often rival fine jade, for which
it is sometimes mistaken. Cut into cabochons (smooth domed gems with
flat backs for use in jewelry), it can be as sought after as fine
amethyst.
Unlike emerald which owes its beautiful
green color to the presence of chromium, the color of chrysoprase
is due to trace amounts of nickel in the structure. The nickel reportedly
occurs as platelets of the talc-like mineral willemseite. Chrysoprase
results from the deep weathering or lateritization of nickeliferous
serpentinites or other ultramafic ophiolite rocks. In the Australian
deposits, chrysoprase occurs as veins and nodules with brown goethite
and other iron oxides in the magnesite-rich saprolite below an iron
and silica cap.
As with all forms of quartz, chrysoprase
has a hardness of 6 - 7 on the Mohs hardness scale and a conchoidal
fracture like flint.
The best known sources of chrysoprase
are Queensland, Western Australia, Germany, Poland, Russia, Arizona,
California, and Brazil.
Diamond
Diamond is the hardest known natural
material and one of the two best known forms (or allotropes)
of carbon, whose hardness and high dispersion of light make it useful
for industrial applications and jewelry. (The other equally well known
allotrope is graphite.) Diamonds are specifically renowned as a mineral
with superlative physical qualities -- they make excellent abrasives
because they can be scratched only by other diamonds, Borazon, ultrahard
fullerite, or aggregated diamond nanorods, which also means they hold
a polish extremely well and retain luster. About 130 million carats
(26,000 kg) are mined annually, with a total value of nearly USD $9
billion. About 100 tons are synthesized annually.
The name “diamond” derives
from the ancient Greek adamas (αδάμας;
“invincible”). They have been treasured as gemstones since
their use as religious icons in India at least 2,500 years ago --
and usage in drill bits and engraving tools also dates to early human
history. Popularity of diamonds has risen since the 19th century because
of increased supply, improved cutting and polishing techniques, growth
in the world economy, and innovative and successful advertising
campaigns. They are commonly judged
by the “four Cs”: carat, clarity, color,
and cut. Although synthetic diamonds are produced each year
at nearly four times the rate of natural diamonds, the vast majority
of synthetic diamonds produced are small imperfect diamonds suitable
only for industrial-grade use.
Roughly 49% of diamonds originate
from central and southern Africa, although significant sources of
the mineral have been discovered in Canada, India, Russia, Brazil,
and Australia. They are generally mined from volcanic pipes, which
are deep in the Earth where the high pressure and temperature enables
the formation of the crystals. The mining and distribution of natural
diamonds are subjects of frequent controversy -- such as with concerns
over the sale of conflict diamonds by African paramilitary
groups.
Material
properties
A diamond is a transparent crystal
of tetrahedrally bonded carbon atoms. Diamonds have been adapted for
many uses because of the material's exceptional physical characteristics.
Most notable are its extreme hardness of diamond, its high dispersion
index, and high thermal conductivity.
Mechanical
properties
Crystal
structure
The conventional unit cell of the
diamond crystal structure.
Diamonds
typically crystallize in the face-centered cubic crystal system(space
group)and consist of tetrahedrally bonded carbon atoms. The unit cell
of diamond has a two atom basis at 0, 0,0) and (1/4,1/4,1/4), which
means half of the atoms are at lattice points and the other half are
offset by (1/4,1/4,1/4), where 1 is the length of a side of the unit
cell. Diamond's density is 3.52 g·cm−3.
Lonsdaleite is a polymorph of diamond
(and a distinct mineral species) that crystallizes with hexagonal
symmetry. It is rarely found in nature but is characteristic of synthetic
diamonds. A cryptocrystalline variety of diamond is called carbonado.
A colorless, grey or black diamond with a tiny radial structure is
a spherulite.
Hardness
The atomic connectivtity of the carbon
atoms gives the gem its hardness
Diamond is the hardest natural material
known, scoring 10 on the relative Mohs scale of mineral hardness and
having an absolute hardness value of between 90, 167, and 231 gigapascals
in various tests. Diamond's hardness has been known since antiquity,
and is the source of its name. However, aggregated diamond nanorods,
an allotrope of carbon first synthesized in 2005, are now believed
to be even harder than diamond.
The hardest diamonds in the world
are from the New England area in New South Wales, Australia. These
diamonds are generally small, perfect to semiperfect octahedra, and
are used to polish other diamonds.
Uses in Industry
Industrial use of diamonds has historically
been associated with their hardness; this property makes diamond the
ideal material for cutting and grinding tools. It is one of the most
known and most useful of more than 3,000 known minerals. As the hardest
known naturally occurring material, diamond can be used to polish,
cut, or wear away any material, including other diamonds. Common industrial
adaptations of this ability include diamond-tipped drill bits and
saws, or use of diamond powder as an abrasive. Other specialized applications
also exist or are being developed, including use as semiconductors:
some blue diamonds are natural semiconductors, in contrast to most
other diamonds, which are excellent electrical insulators. Industrial-grade
diamonds are either unsuitable for use as gems or synthetically produced,
which lowers their price and makes their use economically feasible.
Industrial applications, especially as drill bits and engraving tools,
also date to ancient times.
The hardness of diamonds also contributes
to its suitability as a gemstone. Because it can only be scratched
by other diamonds, it maintains its polish extremely well, keeping
its luster over long periods of time. Unlike many other gems, it is
well-suited to daily wear because of its resistance to scratching
-- perhaps contributing to its popularity as the preferred gem in
an engagement ring or wedding ring, which are often worn every day.
Toughness
Unlike hardness, which only denotes
resistance to scratching, diamond's toughness is good in cleavage
directions, exceptional in all other directions. Toughness relates
to a material's ability to resist breakage from forceful impact. As
with any material, the macroscopic geometry of a diamond contributes
to its resistance to breakage. Diamond is therefore more fragile in
some orientations than others.
Color
Diamonds can occur in nearly any
color, though yellow and brown are by far the most common. "Black"
diamonds are not truly black, but rather contain numerous dark inclusions
that give the gems their dark appearance. Diamonds with a detectable
hue other than yellow or brown are known as colored diamonds.
If the color is strong enough, a stone may be referred to as a fancy
colored diamond by the trade. Colored diamonds contain impurities
or structural defects that cause the coloration, while pure or nearly
pure diamonds are transparent and colorless. Most diamond impurities
replace a carbon atom in the crystal lattice. The most common impurity,
nitrogen, causes a slight to intense yellow coloration depending upon
the type and concentration of nitrogen present. The color scale for
colorless diamonds goes from 'D' (colorless) to 'Z' (dark yellow).
Natural
history
Formation
Diamonds are formed by prolonged
exposure of carbon bearing materials to high pressure and temperature.
On Earth, the formation of diamonds is possible because there are
regions deep within the Earth that are at a high enough pressure and
temperature that the formation of diamonds is thermodynamically favorable.
Under continental crust, diamonds form starting at depths of about
150 kilometers (90 miles), where pressure is roughly 5 gigapascals
and the temperature is around 1200 degrees Celsius (2200 degrees Fahrenheit).
Diamond formation under oceanic crust takes place at greater depths
because of higher temperatures, which require higher pressure for
diamond formation. Long periods of exposure to these high pressures
and temperatures allow diamond crystals to grow larger.
The slightly misshapen octahedral shape of this rough diamond crystal
in matrix is typical of the mineral. Its lustrous faces also indicate
that this crystal is from a primary deposit.
Through studies of carbon isotope
ratios (similar to the methodology used in carbon dating, except with
the stable isotopes C-12 and C-13), it has been shown that the carbon
found in diamonds comes from both inorganic and organic sources. Some
diamonds, known as harzburgitic,
are formed from inorganic carbon originally found deep in the Earth's
mantle. In contrast, eclogitic diamonds contain organic carbon
from organic detritus that has been pushed down from the surface of
the Earth's crust through subduction (see plate tectonics) before
transforming into diamond. These two different source carbons have
measurably different 13C:12C ratios. Diamonds that have come to the
Earth's surface are generally very old, ranging from under 1 billion
to 3.3 billion years old.
Diamonds occur most often as euhedral
or rounded octahedra and twinned octahedra known as macles
or maccles. As diamond's crystal structure has a cubic arrangement
of the atoms, they have many facets that belong to a cube, octahedron,
rhombicosidodecahedron, tetrakis hexahedron or disdyakis dodecahedron.
The crystals can have rounded off and unexpressive edges and can be
elongated. Sometimes they are found grown together or form double
"twinned" crystals grown together at the surfaces of the
octahedron. This is all due to the conditions in which they form.
Diamonds (especially those with rounded crystal faces) are commonly
found coated in nyf, an opaque gum-like skin.
Diamonds can also form in other natural
high-pressure, high-temperature events. Very small diamonds, known
as microdiamonds or nanodiamonds, have been found
in impact craters where meteors strike the Earth and create shock
zones of high pressure and temperature where diamond formation can
occur. Microdiamonds are now used as one indicator of ancient meteorite
impact sites.
Gemological
characteristics
The use of diamonds as gemstones
of decorative value is the most familiar use to most people today,
and is also the earliest use, with decorative use of diamonds stretching
back into antiquity. The dispersion of white light into a rainbow
of colors, known in the trade as fire, is the other primary characteristic
of gem diamonds, and has been highly prized throughout history. Over
time, especially since around 1900, experts in the field of gemology
have developed methods of characterizing diamonds and other gemstones
based on the characteristics most important to their value as a gem.
Four characteristics, known informally as the four Cs, are now commonly
used as the basic descriptors of diamonds: these are carat, clarity,
color, and cut.
Most gem diamonds are traded on the
wholesale market based on single values for each of the four Cs; for
example knowing that a diamond is rated as 1.5 carats, VS2 clarity,
F color, excellent cut, is enough to reasonably establish an expected
price range. More detailed information from within each characteristic
can then be used to determine actual market value for individual stones.
Consumers who purchase individual diamonds are often advised to use
the four Cs to pick the diamond that is "right" for them;
to these is sometimes added the "fifth C" of cost.
Other characteristics not described
by the four Cs can and do influence the value or appearance of a gem
diamond. These characteristics include physical characteristics such
as the presence of fluorescence, as well as data on a diamond's history
including its source and which gemological institute performed evaluation
services on the diamond. Cleanliness also dramatically affects a diamond's
beauty.
There are four major gemological
associations which "certify" diamonds: that is, define the
four Cs of a diamond. While carat weight and cut angles are mathematically
defined, the clarity and color are judged by the trained human eye
and are therefore open to slight variance in interpretation.
Gemological Institute of America
(GIA) was the first laboratory to issue modern diamond reports, and
holds the highest reputation amongst gemologists for its consistent,
conservative grading.
American Gemological Society (AGS)
is not as widely recognized nor as old as the GIA, but garners an
equally high reputation.
International Gemological Laboratory
(IGL) is a generally respected laboratory but suffers from a negative
industry reputation for its grading practices, which are perceived
by critics as being either less conservative or less consistent than
the GIA and AGS.
European Gemological Laboratory USA
(EGLUSA) Good reputation among the trade for consistent and fair grading.
Not as widely known as GIA or AGS.
Carat
The carat weight measures
the mass of a diamond. One carat is defined as a fifth of a gram,
or exactly 200 milligrams (about 0.007 ounce). The point
unit -- equal to one one-hundredth of a carat (0.01 carat, or 2 mg
-- is commonly used for diamonds of less than one carat. All else
being equal, the value of a diamond increases exponentially in relation
to carat weight, since larger diamonds are both rarer and more desirable
for use as gemstones.
The price per carat does not increase
smoothly with increasing size. Instead, there are sharp jumps around
milestone carat weights, as demand is much higher for diamonds weighing
just more than a milestone than for those weighing just less. As an
example, a 0.95 carat diamond may have a significantly lower price
per carat than a comparable 1.05 carat diamond, because of differences
in demand.
Clarity
Clarity is a measure of internal
defects of a diamond called inclusions. Inclusions may be crystals
of a foreign material or another diamond crystal, or structural imperfections
such as tiny cracks that can appear whitish or cloudy. The number,
size, color, relative location, orientation, and visibility of inclusions
can all affect the relative clarity of a diamond. The Gemological
Institute of America (GIA) and others have developed systems to grade
clarity, which are generally based on those inclusions which are visible
to a trained professional when a diamond is viewed from above, under
10x magnification.
Diamonds become increasingly rare
when considering higher clarity gradings. Only about 20 percent of
all diamonds mined have a clarity rating high enough for the diamond
to be considered appropriate for use as a gemstone; the other 80 percent
are relegated to industrial use. Of that top 20 percent, a significant
portion contains a visible inclusion or inclusions. Those that do
not have a visible inclusion are known as "eye-clean" and
are preferred by most buyers, although visible inclusions can sometimes
be hidden under the setting in a piece of jewelry.
Most inclusions present in gem-quality
diamonds do not affect the diamonds' performance or structural integrity.
However, large clouds can affect a diamond's ability to transmit and
scatter light. Large cracks close to or breaking the surface may reduce
a diamond's resistance to fracture.
Diamonds are graded by the major
societies on a scale ranging from flawless to imperfect.
Color
A chemically pure and structurally
perfect diamond is perfectly transparent with no hue, or color. However,
in reality almost no gem-sized natural diamonds are absolutely perfect.
The color of a diamond may be affected by chemical impurities and/or
structural defects in the crystal lattice. Depending on the hue and
intensity of a diamond's coloration, a diamond's color can either
detract from or enhance its value. For example, most white diamonds
are discounted in price as more yellow hue is detectable, while intense
pink or blue diamonds (such as the Hope Diamond) can be dramatically
more valuable.
Most diamonds used as gemstones are
basically transparent with little tint, or white diamonds.
The most common impurity, nitrogen, replaces a small proportion of
carbon atoms in a diamond's structure and causes a yellowish to brownish
tint. This effect is present in almost all white diamonds; in only
the rarest diamonds is the coloration due to this effect undetectable.
The GIA has developed a rating system for color in white diamonds,
from "D" to "Z" (with D being "colorless"
and Z having a bright yellow coloration), which has been widely adopted
in the industry and is universally recognized, superseding several
older systems once used in different countries. The system uses a
benchmark set of either natural diamonds of known color grade, or
precision-crafted cubic zirconia; test lighting conditions are also
standardized and carefully controlled. Diamonds with higher color
grades are rarer, in higher demand, and therefore more expensive,
than lower color grades. Oddly enough, diamonds graded Z are also
rare, and the bright yellow color is also highly valued. Diamonds
graded D-F are considered "colorless", G-J are considered
"near-colorless", K-M are "slightly colored".
N-Y usually appear light yellow or brown.
In contrast to yellow or brown hues,
diamonds of other colors are much rarer and more valuable. While even
a pale pink or blue hue may increase the value of a diamond, more
intense coloration is usually considered more desirable and commands
the highest prices. A variety of impurities and structural imperfections
cause different colors in diamonds, including yellow, pink, blue,
red, green, brown, and other hues. Diamonds with unusual or intense
coloration are sometimes labeled "fancy" by the diamond
industry. Intense yellow coloration is considered one of the fancy
colors, and is separate from the color grades of white diamonds. Gemmologists
have developed rating systems for fancy colored diamonds, but they
are not in common use because of the relative rarity of colored diamonds.
Cut
Diamond cutting is the art and science
of creating a gem-quality diamond out of mined rough. The cut of a
diamond describes the manner in which a diamond has been shaped and
polished from its beginning form as a rough stone to its final gem
proportions. The cut of a diamond describes the quality of workmanship
and the angles to which a diamond is cut. Often diamond cut is confused
with "shape".
There are mathematical guidelines for the angles and length ratios
at which the diamond is supposed to be cut in order to reflect the
maximum amount of light. Round brilliant diamonds, the most common,
are guided by these specific guidelines, though fancy cut stones are
not able to be as accurately guided by mathematical specifics.
The techniques for cutting diamonds
have been developed over hundreds of years, with perhaps the greatest
achievements made in 1919 by mathematician and gem enthusiast Marcel
Tolkowsky. He developed the round brilliant cut by calculating the
ideal shape to return and scatter light when a diamond is viewed from
above. The modern round brilliant has 57 facets (polished faces),
counting 33 on the crown (the top half), and 24 on the pavilion
(the lower half). The girdle is the thin middle part. The function
of the crown is to diffuse light into various colours and the pavilion's
function to reflect light back through the top of the diamond.
Tolkowsky defines the ideal dimensions
to have:
Table percentage (table diameter
divided by overall diameter) = 53%.
Depth percentage (Overall depth divided by the overall diameter) =
59.3%.
Pavilion Angle (Angle between the girdle and the pavilion) = 40.75°.
Crown Angle (Angle between the girdle and the crown) = 34.5°.
Pavilion Depth (Depth of pavilion divided by overall diameter) = 43.1%.
Crown Depth (Depth of crown divided by crown diameter) = 16.2%.
A thin girdle is required in reality
in order to prevent the diamond from easily chipping in the setting.
A normal girdle should be about 1% - 2% of the overall diameter.
Shape
Diamonds do not show all of their
beauty as rough stones; instead, they must be cut and polished to
exhibit the characteristic fire and brilliance that diamond gemstones
are known for. Diamonds are cut into a variety of shapes that are
generally designed to accentuate these features.
Cuts are influenced heavily by fashion:
the baguetta cut – which accentuates a diamond’s luster
and downplays its fire – was all the rage during the Art Deco
period, whereas the princess cut – which accentuates a diamond’s
fire rather than its luster – is currently gaining popularity.
The princess cut is also popular amongst diamond cutters: of all the
cuts, it wastes the least of the original crystal. The past
decades have seen the development of new diamond cuts, often based
on a modification of an existing cut. Some of these include extra
facets. These newly developed cuts are viewed by many as more
of an attempt at brand differentiation by diamond sellers, than actual
improvements to the state of the art.
Quality
The quality of a diamond's cut is
widely considered the most important of the four Cs in determining
the beauty of a diamond; indeed, it is commonly acknowledged that
a well-cut diamond can appear to be of greater carat weight, and have
clarity and colour appear to be of better grade than they actually
are. The skill with which a diamond is cut determines its ability
to reflect and refract light.
In addition to carrying the most
importance to a diamond's quality as a gemstone, the cut is also the
most difficult to quantitatively judge. A number of factors, including
proportion, symmetry, and the relative angles of various facets, are
determined by the quality of the cut and can affect the performance
of a diamond. A poorly cut diamond with facets cut only a few degrees
out of alignment can result in a poorly performing stone. For a round
brilliant cut, there is a balance between "brilliance" and
"fire." When a diamond is cut for too much "fire,"
it looks like a cubic zirconia, which gives off much more "fire"
than real diamond. A well-executed round brilliant cut should reflect
light upwards and make the diamond appear white when viewed from the
top. An inferior cut will produce a stone that appears dark at the
center and in some extreme cases the ring settings may show through
the top of the diamond as shadows.
Several different theories on the
"ideal" proportions of a diamond have been and continue
to be advocated by professional gemologists. Recently, there has been
a shift away from grading cut by the use of various angles and proportions
toward measuring the performance of a cut stone. A number of specially
modified viewers and machines have been developed toward this end.
They included the FireScope, SymmetriScope or IdealScope (tests for
light leakage, light return and proportions), Hearts and Arrows Viewer
(test for "hearts and arrows" characteristic pattern observable
on stones exhibiting high symmetry), GemEx BrillianceScope (tests
for direct light performance results of a diamond), Isee2 Beauty Evaluator
(tests for diffused light performance results for round or octagonal
diamonds), and ASET (test for AGS cut grade). These viewers and machines
often help consumers determine the light performance results of the
diamond in addition to the traditional 4 C's. Along with this shift
there are a few companies that provide results on these viewers and
machines in addition to the original 4c's. The GIA has also developed
criteria for grading the cut of round brilliant stones.
The
cutting process
An uncut diamond does not show its
prized optical properties.
The process of shaping a rough diamond into a polished gemstone is
both an art and a science. The choice of cut is often decided by the
original shape of the rough stone, location of the inclusions and
flaws to be eliminated, the preservation of the weight, popularity
of certain shapes amongst consumers and many other considerations.
The round brilliant cut is preferred when the crystal is an octahedron,
as often two stones may be cut from one such crystal. Oddly shaped
crystals such as macles are more likely to be cut in a fancy cut --
that is, a cut other than the round brilliant --which the particular
crystal shape lends itself to.
Even with modern techniques, the
cutting and polishing of a diamond crystal always results in a dramatic
loss of weight; rarely is it less than 50%. Sometimes the cutters
compromise and accept lesser proportions and symmetry in order to
avoid inclusions or to preserve the carat rating. Since the per carat
price of diamond shifts around key milestones (such as 1.00 carat),
many one-carat diamonds are the result of compromising "Cut"
for "Carat." Some jewelry experts advise consumers to buy
a 0.99 carat diamond for its better price or buy a 1.10 carat diamond
for its better cut, avoiding a 1.00 carat diamond which is more likely
to be a poorly cut stone.
Cleaning
Although it is not one of the four
Cs, cleanliness affects a diamond's beauty as much as any
of the four Cs. A clean diamond is more brilliant and fiery than the
same diamond when it is "dirty." Dirt or grease on the top
of a diamond reduces its luster. Water, dirt, or grease on the bottom
of a diamond interferes with the diamond's brilliance and fire. Even
a thin film absorbs some light that could have been reflected to the
person looking at the diamond. Colored dye or smudges can affect the
perceived color of a diamond. Historically, some jewelers' stones
were misgraded because of smudges on the girdle, or dye on the culet.
Current practice is to thoroughly clean a diamond before grading its
color.
Maintaining a clean diamond can sometimes be difficult, as jewelry
settings can obstruct cleaning efforts, and oils, grease, and other
hydrophobic materials adhere well to a diamond's surface. Some jewelers
provide their customers with ammonia-based cleaning kits; ultrasonic
cleaners are also popular.
Cleanliness does not affect the diamond's
market value, as any competent jeweler will clean the diamond before
offering it for sale. However, cleanliness might reflect a diamond's
sentimental value: some jewelers have noted a correlation between
ring cleanliness and marriage quality.
History
Diamonds are thought to have been
first recognized and mined in India, where significant alluvial deposits
of the stone could then be found. The earliest written reference can
be found in the Buddhist text, the Anguttara Nikaya another sanskrit
text, the Arthashastra, which was completed around 296 BCE and describes
diamond's hardness, luster, and dispersion. Diamonds quickly became
associated with divinity, being used to decorate religious icons,
and were believed to bring good fortune to those who carried them.
Ownership was restricted among various castes by color, with only
kings being allowed to own all colors of diamond.
In February 2005, a joint Chinese-U.S.
team of archaeologists reported the discovery of four corundum-rich
stone ceremonial burial axes originating from China's Liangzhu and
Sanxingcun cultures (4000 BCE–2500 BCE) which, because of the
axes' specular surfaces, the scientists believe were polished using
diamond powder Although there are diamond deposits now known
to exist close to the burial sites, no direct evidence of coeval diamond
mining has been found: the researchers came to this conclusion by
polishing corundum using various lapidary abrasives and modern techniques
then comparing the results using an atomic force microscope. At that
scale, the surface of the modern diamond-polished corundum closely
resembled that of the axes; however, the polishes of the latter were
superior.
Diamonds were traded to both the
east and west of India and were recognized by various cultures for
their gemological or industrial uses. In his work Naturalis Historia,
the Roman writer Pliny the Elder noted diamond's ornamental uses,
as well as its usefulness to engravers because of its hardness. In
China, diamonds seem to have been used primarily for engraving jade
and drilling holes in beads. Archaeological evidence from Yemen suggests
that diamonds were used as drill tips as early as the 4th century
BCE. In Europe, however, diamonds disappeared for almost 1,000 years
following the rise of Christianity because of two effects: early Christians
rejected diamonds because of their earlier use in amulets, and Arabic
traders restricted the flow of trade between Europe and India.
Diagram of old diamond cuts showing
the evolution from the most primitive (point cut) to the most advanced
pre-Tolkowsky cut (old European).
Until the late Middle Ages, diamonds
were most prized in their natural octahedral state, perhaps with the
crystal surfaces polished to increase luster and remove foreign material.
Around 1300, the flow of diamonds into Europe increased via Venice's
trade network, with most flowing through the low country ports of
Bruges, Antwerp, and Amsterdam. During this time, the taboo against
cutting diamonds into gem shapes, which was established over 1,000
years earlier in the traditions of India, ended allowing the development
of diamond cutting technology to begin in earnest. By 1375, a guild
of diamond polishers had been established at Nuremberg. Over the following
centuries, various diamond cuts were introduced which increasingly
demonstrated the fire and brilliance that makes diamonds treasured
today: the table cut, the briolette (around 1476),
the rose cut (mid-16th century), and by the mid-17th century,
the Mazarin, the first brilliant cut diamond design. In 1919,
Marcel Tolkowsky developed an ideal round brilliant cut design
that has set the standard for comparison of modern gems; however,
diamond cuts have continued to be refined.
The rise in popularity of diamonds
as gems seems to have paralleled increasing availability through European
history. In the 13th century, King Louis IX of France established
a law that only the king could own diamonds. However, within a century
diamonds were popular gems among the moneyed aristocratic and merchant
classes, and by at latest 1477 had begun to be used in wedding rings.
Popularity continued to rise as new cuts were developed that enhanced
the diamond's aesthetic appeal, and has largely continued unabated
to this day; diamonds have proven popular with all classes in society
as their cost has become within reach. A number of large diamonds
have become historically significant objects, as their inclusion in
various sets of crown jewels and the purchase, sale, and sometimes
theft of notable diamonds, have sometimes become politicized.
Record-holding diamonds
The Cullinan Diamond, part of the
British crown jewels, was the largest gem-quality rough diamond ever
found (1905), at 3,106.75 carats. One of the diamonds cut from it,
Cullinan I or the Great Star of Africa, was formerly the largest gem-quality
cut diamond at 530.2 carats, but now that title has been taken by
the Golden Jubilee (1985), a 545.67 carat, yellow-brown diamond. The
largest flawless and colorless (grade D) diamond is the Centenary
Diamond which weighs 273.85 carats. The Millennium Star is the second
largest (1990) at 203.04 carats.
A
round brilliant cut diamond set in a ring.
The diamond industry
The diamond industry can be broadly
separated into two basically distinct categories: one dealing with
gem-grade diamonds and another for industrial-grade diamonds. While
a large trade in both types of diamonds exists, the two markets act
in dramatically different ways.
Gem
diamond industry
A large trade in gem-grade diamonds
exists. Unlike precious metals such as gold or platinum, gem diamonds
do not trade as a commodity: there is a substantial mark-up in the
sale of diamonds, and there is not a very active market for resale
of diamonds. One hallmark of the trade in gem-quality diamonds is
its remarkable concentration: wholesale trade and diamond cutting
is limited to a few locations (most importantly New York, Antwerp,
London, Tel Aviv, Amsterdam and Surat). and a single company -- De
Beers -- controls a significant proportion of the trade in diamonds.
They are based in Johannesburg, South Africa and London, England.
The production and distribution of
diamonds is largely consolidated in the hands of a few key players,
and concentrated in traditional diamond trading centers (the most
important being Antwerp). The De Beers company holds a clearly
dominant position in the industry, and has done so since soon after
its founding in 1888 by the British imperialist Cecil Rhodes. De Beers
owns or controls a significant portion of the world's rough diamond
production facilities (mines) and distribution channels for gem-quality
diamonds. The company and its subsidiaries own mines that produce
some 40 percent of annual world diamond production. At one time it
was thought over 80 percent of the world's rough diamonds passed through
the Diamond Trading Company (DTC, a subsidiary of De Beers) in London,
but presently the figure is estimated at less than 50 percent. De
Beers used its monopoly position to establish strict price controls,
and market diamonds directly to consumers in world markets.
Industrial
diamond industry
The market for industrial-grade diamonds
operates much differently from its gem-grade counterpart. Industrial
diamonds are valued mostly for their hardness and heat conductivity,
making many of the gemological characteristics of diamond, including
clarity and color, mostly irrelevant. This helps explain why 80% of
mined diamonds (equal to about 100 million carats or 20,000 kg annually),
unsuitable for use as gemstones and known as bort, are destined for
industrial use. In addition to mined diamonds, synthetic diamonds
found industrial applications almost immediately after their invention
in the 1950s; another 400 million carats (80,000 kg) of synthetic
diamonds are produced annually for industrial use -- nearly four times
the mass of natural diamonds mined over the same period.
The dominant industrial use of diamond
is in cutting, drilling, grinding, and polishing. Most uses of diamonds
in these technologies do not require large diamonds; in fact, most
diamonds that are gem-quality except for their small size, can find
an industrial use. Diamonds are embedded in drill tips or saw blades,
or ground into a powder for use in grinding and polishing applications.
Specialized applications include use in laboratories as containment
for high pressure experiments, high-performance bearings, and limited
use in specialized windows.
With the continuing advances being
made in the production of synthetic diamond, future applications are
beginning to become feasible. Garnering much excitement is the possible
use of diamond as a semiconductor suitable to build microchips from,
or the use of diamond as a heat sink in electronics. Significant research
efforts in Japan, Europe, and the United States are under way to capitalize
on the potential offered by diamond's unique material properties,
combined with increased quality and quantity of supply starting to
become available from synthetic diamond manufacturers.
Diamond
Industry organisations
World Federation of Diamond Bourses
(WFDB).
The WFDB was founded in 1947 to unite
and to provide bourses trading in rough and polished diamonds and
precious stones, with a common set of trading practice. The WFDB provides
a legal framework and convenes to enact regulations for its 25 member
diamond bourses.
International Diamond Manufacturers
Association (IDMA)
IDMA represents the interests of various manufaturers associations,
with respect to current issues concerning the world diamond industry.
World Diamond Council (WDC)
The WDC is a joint committee that
was formed by the WFDB and IDMA to ensure the development, implementation
and oversight of a tracking system for the export and import of rough
diamonds to prevent the exploitation of diamonds for illicit purposes
such as war and inhumane acts.
International Diamond Council (IDC)
A joint committee appointed by The
World Federation of Diamond Bourses (WFDB) and the International Diamond
Manufacturers Association (IDMA) to create an international standard
for rules, working methods and nomenclature for diamond grading laboratories.
Diamond
supply chain
The diamond supply chain is controlled
by a limited number of powerful businesses, and is also highly concentrated
in a small number of locations around the world. In fact, the amount
of power which De Beers has consolidated historically prevented it
from direct trade with the United States, as its trade practices led
to an indictment for violating antitrust regulations (the case was
settled in 2004). The concentration of power only loosens at the retail
level, where diamonds are sold by a limited number of distributors,
known as sightholders, to jewelers around the world.
Sources
Historically diamonds were known
to be found only in alluvial deposits in southern India; India led
the world in diamond production from the time of their discovery in
approximately the 9th century BCE to the mid-18th century CE, but
the commercial potential of these sources has been exhausted. The
first non-Indian diamond source was found in Brazil in 1725. While
no commercial diamond production exists in the US, Arkansas is the
only state to have a verifiable source of diamonds. Today, most commercially
viable diamond deposits are in Africa, notably in South Africa, Namibia,
Botswana, the Democratic Republic of Congo, Angola, Tanzania and Sierra
Leone. There are also commercial deposits being actively mined in
the Northwest Territories of Canada, Siberia (mostly in Yakutia territory,
for example Mir pipe and Udachnaya pipe), Brazil, and in Northern
and Western Australia. Diamond prospectors continue to search the
globe for diamond-bearing kimberlite and lamproite pipes.
In some of the more politically unstable
central African and west African countries, revolutionary groups have
taken control of diamond mines, using proceeds from diamond sales
to finance their operations. Diamonds sold through this process are
known as conflict diamonds or blood diamonds. In
response to public concerns that their diamond purchases were contributing
to war and human rights abuses in central Africa and west Africa,
the diamond industry and diamond-trading nations introduced the Kimberley
Process in 2002, which is aimed at ensuring that conflict diamonds
do not become intermixed with the diamonds not controlled by such
rebel groups. The Kimberley Process provides documentation and certification
of diamond exports from producing countries to ensure that the proceeds
of sale are not being used to fund criminal or revolutionary activities.
Although the Kimberley Process has been somewhat successful in limiting
the number of conflict diamonds entering the market, conflict diamonds
smuggled to market continue to persist to some degree (approx. 1%
of diamonds traded today are possible conflict diamonds[citation needed]).
According to the 2006 book, The Heartless Stone, two major
flaws still hinder the effectiveness of the Kimberley Process: the
relative ease of smuggling diamonds across African borders and given
phony histories, and the violent nature of diamond mining in nations
which are not in a technical state of war and whose diamonds are therefore
considered "clean".
Currently, gem production totals
nearly 30 million carats (6,000 kg) of cut and polished stones annually,
and over 100 million carats (20,000 kg) of mined diamonds are sold
for industrial use each year, as are about 100,000 kg of synthesized
diamond. In 2003, this constituted total production of nearly US$9
billion in value.
Mining
Only a very small fraction of the
diamond ore consists of actual diamonds. The ore is crushed, during
which care has to be taken in order to prevent larger diamonds from
being destroyed in this process and subsequently the particles are
sorted by density. Nowadays, the diamonds are located in the diamond-rich
density fraction with the help of X-ray fluorescence, after which
the final sorting steps are done by hand. Before the use of X-rays
became commonplace, the separation was done with grease belts; diamonds
have a stronger tendency to stick to grease than the other minerals
in the ore.
Distribution
The Diamond Trading Company, or DTC,
is a subsidiary of De Beers and markets rough diamonds produced both
by De Beers mines and other mines from which it purchases rough diamond
production. DTC performs sophisticated sorting of rough diamonds into
over 16,000 categories, and then sells bulk lots of rough diamonds
to a limited number of sightholders a few times a year.
Once purchased by sightholders, diamonds
are cut and polished in preparation for sale as gemstones. The cutting
and polishing of rough diamonds is a specialized skill that is concentrated
in a limited number of locations worldwide. Traditional diamond cutting
centers are Antwerp, Amsterdam, Johannesburg, New York, and Tel Aviv.
Recently, diamond cutting centers have been established in China,
India, and Thailand. Cutting centers with lower costs of labor, notably
Surat in Gujarat, India, handle a larger number of smaller carat diamonds,
while smaller quantities of larger or more valuable diamonds are more
likely to be handled in Europe or North America. Demonstrating this,
India produces 90% of all cut and polished diamonds by number, but
only 55% by value. The recent expansion of this industry in India,
employing low cost labor, has allowed smaller diamonds to be prepared
as gems than was previously economically feasible.
Diamonds which have been prepared
as gemstones are sold on diamond exchanges called bourses.
There are 24 registered diamond bourses. This is the final tightly
controlled step in the diamond supply chain; wholesalers and even
retailers are able to buy relatively small lots of diamonds at the
bourses, after which they are prepared for final sale to the consumer.
Synthetics, simulants, and
enhancements
It is important to distinguish that
a synthetic diamond is a true diamond created by a technological process,
whereas a diamond simulant is defined as a non-diamond material that
is used to simulate the appearance of a true diamond.
The gemological and industrial uses
of diamond have created a large demand for raw stones. A portion of
this demand is now being met by synthetic diamonds, artificially-made
diamonds which have similar properties to natural diamonds. This process
has historically produced industrial-grade diamonds, but synthetic
diamond producers have recently begun to produce diamonds with high
enough quality to penetrate the gem diamond market. Diamonds have
been manufactured synthetically for over fifty years.
A diamond's gem quality, which is
not as dependent on material properties as industrial applications,
has invited both imitation and the invention of procedures to enhance
the gemological properties of natural diamonds. Materials which have
similar gemmological characteristics to diamond but are not real mined
or synthetic diamond are known as diamond simulants. The
most familiar diamond simulant to most consumers is cubic zirconia
(commonly abbreviated as CZ); recently moissanite has also gained
cachet as a popular diamond simulant. Both CZ and moissanite are synthetically
produced for use as a diamond simulant. Diamond enhancements are specific
treatments, performed on natural diamonds (usually those already cut
and polished into a gem), which are designed to better the gemological
characteristics of the stone in one or more ways. These include laser
drilling to remove inclusions, application of sealants to fill cracks,
treatments to improve a white diamond's color grade, and treatments
to give fancy color to a white diamond.
Currently, trained gemologists with
appropriate equipment are able to distinguish natural diamonds from
all synthetic and simulant diamonds, and identify all enhanced natural
diamonds. The established natural diamond industry has a vested interest
in maintaining the distinction between natural diamonds and other
diamonds, and has made significant investments toward that end. However,
as manufacturing technology improves, synthetic diamonds may become
indistinguishable from natural diamonds, and new techniques for creating
and treating simulants (such as coating them with a very thin diamond-like
layer of carbon) are making it increasingly difficult to distinguish
simulants from real diamonds.
Diamond
and spiritualism
Because of their extraordinary physical
properties, diamonds have been used symbolically since near the time
of their first discovery. Perhaps the earliest symbolic use of diamonds
was as the eyes of Hindu devotional statues. In Hinduism Indra uses
Vajrayudham or the thunderbolt as his primary weapon. Vajra is the
word for diamond and ayudham means weapon in Sanskrit. The diamonds
themselves were thought to be endowments from the gods and were therefore
cherished. The point at which diamonds began to be associated with
divinity is not known, but early texts indicate that it was recognized
in India since at least 400 BCE. It is said the Greeks believed diamonds
were tears of the gods; the Romans believed they were splinters of
fallen stars. Many long dead cultures have sought to explain diamond's
superlative properties through divine or mystical affiliations.
In Tibetan Buddhism, also known as
Vajrayana (Diamond Vehicle), diamonds are an important symbol, and
the Diamond Sutra is one of the most popular texts.
In Western culture, diamonds are
the traditional emblem of fearlessness and virtue, but have also often
associated with power, wealth, crime and misfortune. Today, diamonds
are used to symbolize eternity and love, being often seen adorning
engagement rings and sometimes wedding rings as well.. Inaccessibility
of diamonds to the vast majority of the population limited the popularity
of diamonds as betrothal jewels during this period.
Symbolism in the Occult
Historically, and in occultist myths,
it has been claimed that diamonds possess several supernatural powers:
A diamond gives victory to a person
who carries it bound on his left arm, no matter the number of enemies.
Panics, Pestilences, enchantments,
all fly before it; hence, it is good for sleepwalkers and the insane.
It deprives lodestone and magnets of their virtue (i.e., ability to
attract iron). Arabic diamonds are said to attract iron greater than
a magnet.
A diamond's hardiness can only be broken by smearing it with fresh
goat's blood.
