Gemstone

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, or petrified organic matter that, when cut or faceted and polished, is collectible or can be used in jewelry. Some gemstones, such as single-crystal rhodochrosite, are beautiful and considered precious but are too soft or fragile to be used in jewelry. These stones are often exhibited in museums and sought by collectors.

• Others are organic, such as amber, which is fossilised tree resin and jet, a form of coal.

Characteristics and classification

Gemstones are made of various materials. For instance, diamonds are made of carbon (C), rubies of aluminum oxide (Al₂O₃, or corundum). Also, many gems are crystals, with structures such as cubic, trigonal, or monoclinic. Gemologists classify gemstones according to their chemical composition and crystal structure. Another term used by gemologists is "crystal habit," which is 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 that belongs to the spinel or hematite group. Emerald (green), aquamarine (blue), bixbite (red), goshenite (colorless), heliodor (yellow), and morganite (pink) are all varieties of the mineral species beryl.

Properties of gems include their refractive index, dispersion of light, specific gravity (density), hardness, cleavage, fracture, luster, luminescence, and an absorption spectrum (spectrum of light absorbed by the material). If a gemstone contains other material or flaws, they are known as inclusions.

Value

Jewelry made with gem amber

A gemstone is especially prized for its beauty or perfection of appearance. Characteristics that make a stone beautiful or desirable include its color, rarity, durability, size, and any unusual optical phenomena. Sometimes, the form of the natural crystal and the presence of an interesting inclusion, such as a fossil, will enhance the stone's value.

Diamond is highly prized as a gemstone because it is the hardest naturally occurring substance known and, when faceted, can reflect light with fire and sparkle. Diamonds, however, are far from rare, as millions of carats are mined each year.

Traditionally, common gemstones were grouped as precious stones (cardinal gems) and semi-precious stones. The former category was largely determined by rarity and a history of ecclesiastical, devotional, or ceremonial use. Only five types of gemstones were considered precious: diamond, ruby, sapphire, emerald, and amethyst. Currently, gemologists consider all gems as precious, although four of the five original "cardinal gems" are usually (but not always) regarded as the most valuable. The value of amethyst has dropped ever since huge quantities were discovered in Brazil.

Some gemstones are so rare and unusual that that they are scarcely known except to connoisseurs. They include andalusite, axinite, cassiterite, clinohumite, and iolite.

Synthetic and artificial gemstones

Some gemstones are manufactured to imitate others. For example, cubic zirconia is a synthetic diamond simulant, composed of zirconium oxide. Such imitations copy the look and color of the real stone but possess different chemical and physical characteristics. True synthetic gemstones, however, are not necessarily imitation. For example, diamonds, rubies, sapphires, and emeralds have been manufactured in laboratories, with chemical and physical properties that are very nearly identical to those of the genuine stones. Synthetic corundum stones, including ruby and sapphire, are quite common and 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 colored variety, have been manufactured.

Types of gemstones

There are over 130 species of minerals that have been cut into gems. Of these, about 50 species, listed below, are in common use.

• Agate (an aggregate of various forms of quartz, especially chalcedony)
• Alexandrite (and other varieties of chrysoberyl)
• Amethyst (a variety of quartz)
• 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 include:

• Andalusite
• Axinite
• Benitoite
• Bixbyte (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

Organic materials used as gems include:

• Amber
• Bone
• Coral
• Ivory
• Jet (lignite)
• Mother of pearl
• Ammolite (from fossils formed from the shells of extinct ammonites)
• Pearl
• Tortoiseshell

List of famous gemstones

A number of gemstones have gained fame because of their size and beauty or because of the people who owned or wore them. A partial list of famous gemstones follows.

Aquamarines

• The Giant Aquamarine

Diamonds

• The Allnatt Diamond
• The Centenary Diamond
• The Cullinan Diamond, the largest rough gem-quality diamond ever found at 3106.75 carats, also known as the Star of Africa
• The Darya-ye Noor Diamond, the best known diamond of the Iranian Crown Jewels
• The Deepdene
• The Dresden Green Diamond
• The Dudley Diamond
• The Eugenie Blue Diamond
• The Excelsior Diamond
• The Florentine Diamond
• The Golden Jubilee (the largest faceted diamond ever cut, at 545.67 carats)
• The Great Chrysanthemum Diamond
• The Great Mogul Diamond
• The Heart of Eternity Diamond (perhaps the largest Fancy Vivid Blue)
• The Hope Diamond (blue, but supposedly cursed)
• The Hortensia Diamond
• The Idol's Eye
• The Incomparable Diamond
• The Jones Diamond
• The Koh-i-Noor (a very old diamond, mentioned in Baburnama of 1526, is surrounded by legend and believed to be the most precious)
• The Millennium Star (the largest colorless, flawless diamond)
• The Moussaieff Red Diamond (the largest Fancy Vivid Red)
• The Nizam Diamond
• The Ocean Dream Diamond (the only known natural Fancy Deep Blue-Green)
• The Oppenheimer Diamond
• The Orloff (an Indian rose cut, rumored to have served as the eye of a Hindu statue)
• The Paragon Diamond
• The Portuguese Diamond
• The Premier Rose Diamond
• The Pumpkin Diamond (perhaps the largest Fancy Vivid Orange)
• The Red Cross Diamond
• The Regent Diamond
• The Sancy
• The Spirit of de Grisogono Diamond (the world's largest cut Black)
• The Star of the South
• The Steinmetz Pink Diamond (the largest Fancy Vivid Pink)
• The Taylor-Burton Diamond
• The Tiffany Yellow Diamond
• The Vargas

Emeralds

• The Duke of Devonshire
• The Gachala Emerald
• The Mackay Emerald

Opals

• The Andamooka Opal, presented to Queen Elizabeth 2, also known as the Queen's Opal
• The Aurora Australis Opal, considered to be the most valuable black opal
• The Black Prince Opal, originally known as Harlequin Prince
• The Empress of Australia Opal
• The Fire Queen Opal
• The Flame Queen Opal
• The Flamingo Opal
• The Halley's Comet Opal, the world's largest uncut black opal
• The Jupiter Five Opal
• The Olympic Australis Opal, reported to be the largest and most valuable gem opal ever found
• The Pride of Australia Opal, also known as the Red Emperor Opal
• The Red Admiral Opal, also known as the Butterfly Stone

Ruby

• The DeLong Star Ruby
• The Hixon Ruby Crystal
• The Midnight Star Ruby
• The Neelanjali Ruby
• The Rajaratna Ruby
• The Rosser Reeves Ruby

Sapphires

• The Logan Sapphire
• The Queen Marie of Romania Sapphire
• The Ruspoli Sapphire
• The Star of Asia Star Sapphire
• The Star of Bombay, given to Mary Pickford by Douglas Fairbanks, Sr
• The Star of India (gem), the largest and most famous star sapphire in the world
• The Stuart Sapphire

Spinels

• The Black Prince's Ruby, actually a spinel mounted on the Imperial State Crown
• The Samarian Spinel, the world's largest spinel
• The Timur Ruby, believed to be a ruby until 1851

Topaz

• The American Golden Topaz, the largest cut yellow topaz weighing nearly 23000 carats!

See also

• List of minerals
• Lapidary
• Jewelry

References

ISBN links support NWE through referral fees

• Weinstein, Michael, 1958, The World of Jewel Stones, Sheridan House, New York
• The Audubon Society Field Guide to North American Rocks and Minerals, 1978, New York, Alfred A. Knopf ISBN 0394502698
• Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., John Wiley and Sons, New York ISBN 0471805807

External links

• Misleading Gem Names
• Famous diamonds: 261 referred diamonds

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