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What is a Gemstone?
A gemstone is a
mineral or rock
such as lapis lazuli or petrified
material which, when shaped, cut or faceted becomes collectible or is
made into jewellery. Other gemstones are actually organic material.
Amber is just such an example of organic material - tree resin - which
has fossilized. Jet is yet another example of organic material forming
a gemstone. It is a form of coal, believe it or not! Gemstones
to be used for jewelry must have the proper characteristics in order
to be successful. Even though certain gemstones may be considered to
be fabulous looking and would make a wonderful piece of jewelry, if
they do not hold the appropriate characteristics of hardness and
durability, they will never make successful jewellery. Instead, they
may have to spend their lives in museums or in a collectors
showcase.
There are over 130
species of minerals that have been cut into gems with 50 species in
common use. These include:
Agate
- Agate is not a distinct mineral, but rather, an aggregate of various forms of
silica.
It is believed that the stone was first found near the river Achates,
now the Drillo River in Sicily and was named as such.
Alexandrite and other varieties of
chrysoberyl
- The mineral/gemstone
chrysoberyl should not be confused with beryl. Chrysoberyl is
transparent to translucent and sometimes chatoyant. An interesting feature of uncut crystals of chyrsoberyl are
the 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.
Amethyst (originally a "cardinal gem", but now no longer so,
since huge quantities were discovered in Brazil and the price plummeted) - Amethyst
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. 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.
 
Aquamarine (Lat. aqua marina, "water of
the sea") is a gemstone-quality
transparent variety of beryl,
having a delicate blue or blue-green 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.
Chrysocolla
- Chrysocolla is a
mineral of 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. 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.
Diamond
- Diamond
is one of the two best known forms
of carbon, whose hardness and high dispersion of light make it useful for industrial applications and
fabulous jewelry. Diamonds are specifically renowned as a
mineral with superlative physical qualities — they make excellent
abrasives
because they can be scratched only by other diamonds and some
other extremely hard items. As a result of this hardness and
durability, they polish very well and can retain their luster
extremely well...making them a prized gemstone and one of the most
popular for jewelry. It is estimated that there are 130 million
diamond carats
(26,000 kg) mined annually. As for the fake or synthesized carats,
that amount almost quadruples to approximately 100,000 kg per
year. Diamonds are rated based on clarity, colour, cut and carat
size. Read more about the 4 C's of diamond
rating.
Emerald
- Emerald is a
variety of the mineral beryl,
colored green by trace amounts of chromium
and sometimes iron. Emerald, being a gemstone high in demand, based on
its weight, is the most valuable gemstone in the world. However,
emeralds are not all created equal. They all contain inclusions or
fillers which, depending on the amount of filler, decrease the value
of the emerald itself. The base component, beryl has a hardness
of 7.5 on the 10 point Mohs
scale of hardness. This degree of hardness can be greatly affected
by the amounts and quality of the fillers - decreasing the hardness
rating. The colours of the gemstone emerald are probably the reason
for its tremendous popularity. Emeralds come in many shades of a deep,
intense, yet bright green and bluish green.
 
Feldspar is an important group of rock-forming minerals
which make up as much as 60% of the Earth's crust.
Feldspars crystallize
from magma in both intrusive and extrusive
rocks; they occur as compact minerals, as veins, and are also present
in many types of metamorphic rock.
Garnet
- Garnets are most
commonly red in color but can be found in a variety of colors,
including purple, red, orange, yellow, green, brown, black and even
colourless. It seems that the only color missing on that list was
blue. After the discovery in the 1990s of color-change
blue to red/pink material in Bekily, Madagascar, blue garnet became
available. However, color-change garnet gemstones are extremely rare
and maybe the rarest with the exception of uvarovite, which cannot
even be cut.
 
Hematite
- Hematite is a very
common mineral, coloured black to steel or silver-gray, brown to
reddish brown, or red. It is mined as the main ore of iron. Varieties include Bloodstone, Iron Rose,
Kidney Ore, Martite, Paint Ore, Specularite (Specular Hematite),
Rainbow Hematite and Titano-hematite. While the forms of hematite
vary, they all have a rust-red streak. Hematite is harder than pure
iron, but much more brittle. Often referred to as Black Diamonds.
Jade - also known as jadeite or nephrite
- The gemstone jade is an exceptionally durable material. Because of
this, it was originally used for survival purposes, to make necessary
items such as knives, axe heads and certain weapons. When other metals
and stones became more useful for weapons, jade became loved for its
wonderful, bright colour and beauty and was made into jewelry. Jade has a
Mohs hardness of between 6.5 and 7.0. And in case you didn't know, Jade is the
official gemstone of British Columbia, Canada, where it is found in large deposits in the
Lillioet and Cassiar regions.
    
Jasper
- Jasper is yet another form of quartz. It is an impure variety found
in various opaque colours such as red, yellow or brown. Jasper is very
smooth, can be highly polished, and has been used to make decorations,
vases, and as a gemstone on its own.
Kunzite
- Kunzite is a
hard pink gemstone,
a variety of spodumene with the colour coming from manganese.
It was named after George Frederick Kunz, who discovered it in
Connecticut, USA in 1902. Kunzite can be found mined in the following
countries currently: Sweden, Mexico, Canada, USA and Brazil.
Lapis
lazuli
- Lapis lazuli,
also known as just lapis, is a gemstone with one of the longest
and most profound histories of all gemstones, dating back to 5000 BC.
It has been strongly associated with Egypt, having had high praise
from pharoahs. The proof is in the tombs - Lapis lazuli has been found
in many of Egypt's pharaonic tombs, standing out from most other
gemstones used. Naturally beautiful, lapis lazuli is still a very
popular gemstone today.
 
Malachite
- Except for the vibrant
green colour, the properties of malachite are very similar to those of
azurite and aggregates of the two minerals together are frequently
found, although malachite is more common than azurite.
Obsidian
- Obsidian is a
type of naturally occurring glass,
produced by volcanoes when a specific type of lava cools rapidly and freezes without sufficient time for crystal growth.
It is commonly found within the margins
of felsic lava flows, where cooling is more rapid.
Olivine or Peridot - Olivine is usually colored olive-green (hence the
name), though it may alter to a reddish color from the oxidation of
iron. It has a conchoidal fracture and is rather brittle.
Opal
(Girasol) - Opal ranges from colorless through white, milky blue,
gray, red, yellow, green, brown and black. Common opal is truly
amorphous, but precious opal does have a structural element.
   
Pyrite
- It has a slightly
uneven and conchoidal fracture, a hardness
of 6–6.5 (compare that to diamonds at hardness of 10). It is brittle, meaning it breaks or
powders easily. Its metallic luster
and pale-to-normal brass-yellow
hue have earned it the nickname fool's gold, but ironically,
small quantities of actual gold
are sometimes found in pyrite.
Quartz and its varieties, such as
tiger's-eye, citrine, agate, and amethyst is one of the world's most common crustal minerals 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).
   
Ruby
- Ruby is a red
gemstone, a variety of the mineral corundum or aluminum oxide in which the color is caused mainly by
chromium. Its name originates from ruber or rubrum,
Latin
for red. Natural rubies are exceptionally rare, though artificial ones
(sometimes called created ruby) can be manufactured by the Verneuil
process relatively inexpensively. Other varieties of gem-quality
corundum are called sapphires. .
  
Sapphire
- Sapphire is the single-crystal
form of aluminum oxide, a mineral known as corundum. It can be found naturally as
gemstones
or manufactured in large crystal boules
for a variety of applications.
 
Spinel
- It may be colorless,
but is usually various shades of red, blue, green, yellow, brown or
black. There is a unique natural white spinel, now lost, that surfaced
briefly in what is now Sri Lanka. Another famous spinel is the Black
Prince's Ruby in the British Crown
Jewels.
Sugilite
- Sugilite (also
known as luvulite) is a relatively rare pink to purple cyclosilicate mineral.
Tanzanite and other varieties of
zoisite
- It is a popular and valuable gemstone
when cut, although its durability is somewhat lacking; its tendency to
break precludes appropriate use as a ring stone. Tanzanite is noted
for its remarkably strong trichroism,
appearing alternately sapphire blue, violet, and sage-green depending
on crystal
orientation. However, most tanzanite is subjected to artificial heat
treatment to improve its colour: this significantly subdues its
trichroism.
 
Topaz
- Topaz is relatively
hard with a hardness measure of 8. Pure topaz is
transparent but is usually tinted by impurities; typical topaz is wine
or straw-yellow.
They may also be white, gray, green, blue, pink or reddish-yellow
and transparent or translucent. When heated, yellow topaz often
becomes reddish-pink.
It can also be irradiated,
turning the stone a light and distinctive shade of blue. A recent
trend in jewelry is the manufacture of topaz specimens that display
iridescent colors, by applying a thin layer of titanium oxide via physical
vapor deposition.
 
Turquoise
- It is rare and valuable
in finer grades and has been enjoyed as a gemstone for thousands of years owing to its unique hue. In recent
times turquoise—like most other opaque gems—has had its popularity
undermined by the introduction of treatments, imitations, and
synthetics
onto the market, some difficult to detect even by experts.
 
Tourmaline
- Tourmaline has a wide
variety of colours. Usually, iron-rich tourmalines are black to bluish-black to deep
brown, while magnesium-rich varieties are brown to yellow,
and lithium-rich tourmalines are practically any color: blue, green,
red, yellow, pink etc. Rarely, it is colourless. Bi-colored and multi-coloured crystals are relatively common, reflecting variations of
fluid chemistry during crystalisation. Crystals may be green at one
end and pink at the other, or green on the outside and pink inside:
this type is called watermelon
tourmaline. Some forms of tourmaline are dichroic,
in that they appear to change color when viewed from different
directions.
 
Zircon
- The natural color of zircon varies between colorless,
yellow-golden, red, brown or green. Colorless specimens that show gem
quality are a popular substitute for diamond;
these specimens are also known as "Matura diamond" (but note
that cubic zirconia is a completely different synthetic mineral with a
different chemical composition).
Minerals that
infrequently occur in gem quality form:
Artificial or synthetic
materials used as gems include:
High-lead glass
- Glass is a uniform material, usually produced when the viscous molten material
cools very rapidly to below its glass transition temperature, without sufficient time for a regular
crystal lattice to form.
Synthetic cubic
zirconia - Cubic
zirconia (or CZ) is zirconium oxide,
an extremely rare mineral in nature but is widely synthesized for use as
a diamond simulant. The synthesized material is hard, optically flawless and
usually colorless, but may be made in a variety of different colors.
It should not be confused with zircon. Because
of its low cost, durability, and close visual likeness to diamond,
synthetic cubic zirconia has remained the most gemologically
and economically important diamond simulant since 1976.
Its main competition as a synthetic gemstone
is the more recently cultivated material moissanite.
 
Synthetic corundum
- Corundum is the crystalline
form of aluminum oxide and one of the rock-forming minerals.
Corundum is naturally clear, but can have different colors when
impurities are present. Transparent
specimens are used as gems, called ruby
if red,
while all other colors are called sapphire..
Synthetic Spinel
- True spinel has long been found in the gemstone-bearing
gravel of Sri Lanka and in limestones
of Myanmar and Thailand. Its hardness
is 8. It is transparent to opaque with a vitreous
to dull lustre. It may be colorless, but is usually various shades of
red, blue, green, yellow, brown or black. There is a unique natural white spinel, now lost, that surfaced
briefly in what is now Sri Lanka. Another famous spinel is the Black
Prince's Ruby in the British Crown
Jewels.
Synthetic Moissanite
- The word moissanite is a trade name given to silicon
carbide for use in the gemstone business. Naturally occurring moissanite is extremely rare, as it is
not formed naturally in any quantity within the Earth, and thus is
found only in tiny quantities in certain types of meteorite and as
microscopic traces in corundum
deposits and kimberlite. Virtually all of the silicon carbide sold in the world, including
moissanite gemstones, is synthetic. Synthetic moissonite is almost as hard as diamond, with a slightly
higher index of refraction and greater dispersion; these qualities
make SiC a decent and durable diamond simulant. Moissanite's greater dispersion and index of refraction
gives it more fire and brilliance than diamond.
There are a number of
organic materials used as gems, including:
Amber
- Amber is a
fossil resin
much used for the manufacture of ornamental objects. Although not
mineralized it is sometimes considered and used as a gemstone. Most of the world's amber is in the range of 30–90 million years
old. Semi-fossilized resin or sub-fossil amber is called copal.
Bone
- speaks for itself.
Coral
- Corals,
which include sea anemones, typically form colonies of many individuals. Reddish coral is
sometimes used as a gemstone
especially in Tibet.
Pure red coral is known as 'fire coral' and it is very rare because of
the demand for perfect fire coral for jewellery-making purposes.
Ivory
- Ivory is a hard,
white, opaque substance that is the bulk of the teeth and tusks of animals such as the
elephant, hippopotamus, walrus, mammoth, narwhal and more. Prior to the introduction of
some very hard plastics, it was mostly used for billiard balls, piano
keys, buttons and and ornamental items.
Jet
(lignite)
- Jet is a
geological material that is not considered a mineral
in the true sense of the word, but rather, a mineraloid
derived from decaying wood under extreme pressure, thus organic in
origin. The name "jet" is the English word derived from the
French “jaiet”. Jet is black or dark brown but may contain pyrite
inclusions, which have a brassy color and metallic lustre.
Jet is found in one of two forms, hard and soft. "Hard" jet
is the result of the carbon compression and salt water;
"soft" jet is the result of the carbon compression and fresh
water. Jet is easily polished.
The adjective jet-black is perhaps more well-known than is this
mineral from which it is derived.
Mother
of pearl
- Nacre, also
known as mother of pearl, is a naturally-occurring
organic-inorganic composite. Nacre is secreted by the epithelial cells
of the mantle tissue of certain species of mollusk.
In these mollusks, nacre is continually deposited onto the inner
surface of the animal's shell (the iridescent
nacreous layer, commonly known as mother of pearl), both
as a means to smooth the shell itself and as a defense against
parasitic organisms and damaging detritus. Chief sources are the pearl
oyster, found in warm and tropical seas, primarily in Asia;
freshwater pearl mussels, which live in many rivers of the United
States, Europe, and Asia;
and the abalone of California, Japan, and other Pacific regions.
 
Ammolite
- from fossils formed from the shells of extinct ammonites.
Ammolite is a rare and valuable opal-like
organic gemstone
found primarily along the eastern slopes of the Rocky Mountains of the
United States and Canada. It is made of the fossilized
shells of ammonites,
which in turn are composed primarily of aragonite,
the same mineral
that makes up nacreous pearls. It is one of the three biogenic gemstones, the other two being
amber and pearl.
Pearl
- A pearl is a hard, rounded object produced by certain
animals, primarily mollusks such as oysters. Pearls can be used in jewelry and also crushed in cosmetics or paint.
Pearl is valued as a gemstone
and is cultivated or harvested for jewelry. The pearl is also the
birthstone
of June. Pearls fit into two categories: freshwater and saltwater. As
their name implies, freshwater pearls are formed in freshwater mussels
that live in lakes, rivers, ponds and other bodies of fresh water.
Most freshwater cultured pearls sold today come from China. By
contrast, saltwater pearls grow in oysters that live in the ocean,
usually in protected lagoons. Akoya, South Sea and Tahitian are the
three main types of saltwater pearls
. 
Pearls are usually
white, sometimes with a creamy or pinkish tinge, but may be tinted
with yellow, green, blue, brown, purple, or black. Black pearls,
frequently referred to as Black Tahitian Pearls are highly valued
because of their rarity; the culturing process for them dictates a
smaller volume output and can never be mass produced.
 
Some definitions courtesy of: Wikipedia.org. Thanks for this great
information!
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