Gems, Gemstones Directory, Info, Gem, Gem Stone Links & Web Sites @ Tex.in

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).This article is about gemstones as jewelry or decorative art. For other uses of the word see gemstone (disambiguation).

A gemstone is a mineral, rock (such in the case of lapis lazuli), or petrified material that when cut or faceted and polished is collectible or can be used in jewelry. Others are organic (such as amber, which is fossilised tree resin, and jet, a form of coal). Some gemstones which may be generally considered precious or beautiful are too soft or too fragile to be used in jewelry (for example, single-crystal rhodochrosite) but are exhibited in museums and are sought by collectors.

Contents

1 Characteristics and classification

2 Value

3 Treatments applied to gemstones

3.1 Heat

3.2 Radiation

3.3 Waxing/Oiling

3.4 Coatings

4 Factors influencing esteem

5 Synthetic and artificial gemstones

6 Gemstone list

7 See Also

8 External links

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 (C), rubies of aluminium oxide (Al2O3). 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 (green), aquamarine (blue), bixbite (red), goshenite (colorless), heliodor (yellow), and morganite (pink) 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

Jewelry made with gem amberA 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.

Treatments applied to gemstones

Treble clef with gemstonesGemstones 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 or green.

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.

Factors influencing esteem

Factors influencing the esteem in which gems are held are attractiveness, durability, rarity, fashion, light reflection 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:

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 - jadeite and nephrite

Jasper

Kunzite

Lapis lazuli

Malachite

Obsidian

Olivine (Peridot)

Opal (Girasol)

Pyrite

Quartz 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

Minerals that infrequently occur in gem quality form:

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