Gemstone
A gemstone is a
mineral, rock , or
petrified material that when cut or faceted and polished is collectible or can be used in
jewelry. Others are
organic . Some gemstones which may be generally considered precious or beautiful are too soft or too fragile to be used in jewelry but are exhibited in
museums and are sought by collectors.
Encyclopedia
- This article is about gemstones as jewelry or decorative art. For other uses of the word see gemstone .
A
gemstone is a
mineral, rock , or
petrified material that when cut or faceted and polished is collectible or can be used in
jewelry. Others are
organic . Some gemstones which may be generally considered precious or beautiful are too soft or too fragile to be used in jewelry but are exhibited in
museums and are sought by collectors.
Characteristics and classification
Gemstones are described by gemologists using technical specifications. First, what is it made of, or its chemical composition.
Diamonds for example are made of
carbon , rubies of
aluminium oxide . Next, many gems are crystals which are classified by
crystal system such as
cubic or
trigonal or
monoclinic. Another term used is
habit, the form the gem is usually found in. For example diamonds, which have a cubic crystal system, are often found as octahedrons.
Gems are classified into different
groups,
species, and
varieties. For example,
ruby is the red variety of the species
corundum, while any other color of corundum is considered
sapphire.
Emerald ,
aquamarine ,
bixbite , goshenite , heliodor , and morganite are all varieties of the mineral species beryl.
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 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" 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.
Factors influencing esteem
Factors influencing the esteem in which gems are held are attractiveness, durability, rarity, fashion, and size.
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.
Gemstone list
There are over 130 species of minerals that have been cut into gems with 50 species in common use. These include:
Minerals that infrequently occur in gem quality form:
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Artificial or synthetic materials used as gems include:
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There are a number of organic materials used as gems, including:
See Also
- List of fictional gemstones
External links
- - articles describing different gemstones & gemstone related themes.
- - an article describing proper care of gemstones.
