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.

Characteristics and classification

Gemstones are made of various materials. Most gemstones are minerals, which means they are naturally occurring, inorganic materials, each with a particular chemical composition and structure. For instance, diamonds are made of carbon (C), rubies and sapphires are composed of aluminum oxide (Al₂O₃, or corundum). Some gemstones, such as lapis lazuli, are classified as rock—that is, they are composed of mixtures of minerals. Others are made of organic matter. For example, amber corresponds to fossilized tree resin, and jet is a form of coal. If a gemstone is mainly made of a single mineral but contains small but visible quantities of a different mineral or fossil, those "flaws" are known as inclusions.

Many gems are crystals, in which the molecules (or atoms or ions) are packed in regularly ordered patterns (with names such as cubic, trigonal, and monoclinic). Some crystals exhibit a property called twinning, in which two crystals intergrow and share some of their lattice points.

Characteristics of gems include their optical properties such as luster, luminescence (low-temperature emission of light), dispersion of light (separation of different wavelengths of light), refractive index (ratio of the speed of light in the material to that in a vacuum), and absorption spectrum (wavelengths of light absorbed by the material). In addition, gemstones are characterized by their physical properties such as specific gravity (density), hardness (resistance to scratching), type of cleavage (splitting of crystals along definite planes), and fracture (breakage of the material without separation of the parts).

Gemologists classify gemstones based on their chemical composition and crystal structure. According to one system of classification, gems are considered as varieties that are part of certain species and groups. For example, ruby is the red variety of the species corundum that belongs to the spinel group. Emerald (green), aquamarine (blue), bixbite (red), goshenite (colorless), heliodor (yellow), and morganite (pink) are all varieties of the mineral species beryl.

Gemologists also use the term "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.

Value

Jewelry made with gem amber

The value of a gemstone is usually based on its visual attractiveness, rarity, durability, size, and shape. Characteristics that make a stone beautiful include its color and any unusual optical phenomena. In addition, the stone is cut in ways that enhance its optical features. The art of cutting and polishing gemstones is one of the lapidary arts. Usually, the less the number of imperfections in a stone, the more valuable it is considered. Sometimes, however, the presence of an interesting inclusion will increase 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 and other parts of the world.

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

Various gemstones also have practical value, and many of them are now made by artificial processes. For example, diamonds are excellent abrasives and are used for cutting, drilling, engraving, grinding, and polishing. Synthetic sapphires with small amounts of chromium or titanium are used to generate lasers. In the past, jade was used to make knives and weapons, and lapis lazuli was powdered and converted into the pigment ultramarine.

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.

In the United States, the Federal Trade Commission (FTC) has strict guidelines about labeling artificially produced gemstones. According to the FTC, such stones need to be clearly described with such terms as "synthetic," "imitation," "laboratory-created," and so forth. In addition, the created stone may not be given the name of a particular gemstone unless it has "essentially the same optical, physical, and chemical properties as the stone named." [1]

History, symbolism, and beliefs

Gemstones have been known and valued throughout history. Some have been associated with royalty, wealth, and power

• Agate: In Islamic cultures, agates are highly prized. According to tradition, the wearer of an agate ring is believed to be protected from various mishaps and will enjoy longevity. In other traditions, agate is believed to cure the stings of scorpions and the bites of snakes, soothe the mind, prevent disease, promote eloquence, secure the favor of the powerful, and bring victory over enemies.

• Amethyst: Amethyst has been thought to be a symbol of heavenly understanding and of the pioneer in the spiritual and material realms. [Ranking members of the Catholic Church traditionally wear rings set with a large amethyst as part of their office.]

• Emerald: In some cultures, emerald was used as a cure for epilepsy and dysentery, and it was thought to have the power to ward off evil spirits and protect the wearer's chastity.

• Diamond: In early cultures, diamonds were thought to have been endowed by the gods. In Western culture, diamonds have traditionally been associated with virtue and fearlessness, and today they are taken as symbols of eternity and love.

• 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 Sanskrit text Arthasastra, which was completed around 296 B.C.E. 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.

• Diamonds were traded to both the east and west of India and were recognized by various cultures for their gemological or industrial uses.

• Diamonds have also been associated with wealth, crime, and misfortune.

• In early Chinese cultures, jade was regarded as the royal gem, but it was also used to make decorative items and burial suits.

• Lapis lazuli: Lapis lazuli, also known as just lapis, is a stone with one of the longest traditions of being considered a gemstone, with a history stretching back to 5000 B.C.E. Deep blue in color and opaque, this gemstone was highly prized by the pharaohs of ancient Egypt, as can be seen by its prominent use in many of the treasures recovered from pharaonic tombs.

• The Romans believed that lapis was a powerful aphrodisiac. In the Middle Ages, it was thought to keep the limbs healthy, and free the soul from error, envy and fear.

• It was once believed that lapis had medicinal properties. It was ground down, mixed with milk and applied as a dressing for boils and ulcers.

• Many of the blues in painting from medieval Illuminated manuscripts to Renaissance panels were derived from lapis lazuli.

• [Lapis is a rock and not a mineral because it is made up from various other minerals. To be a true mineral it would have one constituent only.]

Types of gemstones

There are over 130 species of minerals that have been cut into gems. Of these, some of the common ones are listed below.

• 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

Gemstones associated with birth months and days

Birthstones

A birthstone is a gemstone culturally associated with the month of a person's birth. Different cultures have historically used many different sets of birthstones. In 1912, Jewelers of America, a national association of jewelers in the United States, officially adopted the following list, which is currently the most widely used list in the United States and many other countries.

• January: garnet
• February: amethyst
• March: aquamarine or bloodstone
• April: diamond
• May: emerald
• June: pearl, moonstone, or alexandrite
• July: ruby
• August: peridot, sardonyx, or sapphire
• September: sapphire
• October: opal or tourmaline
• November: citrine or yellow topaz
• December: turquoise, lapis lazuli, zircon, or blue topaz. In 2002, the American Gem Trade Association added tanzanite to December.

Zodiac stones

An astrological version of birthstones uses the 12 zodiac signs instead of the 12 calendar months. Listed below are the birthstones associated with dates for the tropical Sun signs.

• Aries (March 21 - April 20): Diamond
• Taurus (April 20 - May 21): Sapphire
• Gemini (May 21 - June 20): Spinel
• Cancer (June 21 - July 22): Emerald
• Leo (July 23 - August 22): Ruby
• Virgo (August 23 - September 22): Opal
• Libra (September 23 - October 23): Peridot
• Scorpio (October 24 - November 21): Aquamarine
• Sagittarius (November 22 - December 21): Topaz
• Capricorn (December 22 - January 21): Garnet
• Aquarius (January 20 - February 18): Amethyst and moonstone
• Pisces (February 19 - March 20): Diamond

Birthday stones

A "birthday stone," sometimes used as a synonym for birthstone (see above), is correlated with the day of the week of a person's birth:

• Monday : Pearl
• Tuesday : Garnet
• Wednesday : Cat's eye (chatoyant chrysoberyl)
• Thursday : Emerald
• Friday : Topaz
• Saturday : Sapphire
• Sunday : Ruby

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 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 (the world's largest and most famous star sapphire)
• The Stuart Sapphire

Spinels

• The Black Prince's Ruby (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

Credits

New World Encyclopedia writers and editors rewrote and completed the Wikipedia article in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3.0 License (CC-by-sa), which may be used and disseminated with proper attribution. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation. To cite this article click here for a list of acceptable citing formats.The history of earlier contributions by wikipedians is accessible to researchers here:

• Gemstone  ^history
• List_of_famous_gemstones  ^history
• List_of_famous_diamonds  ^history
• Birthday  ^history
• Agate  ^history
• Lapis_lazuli  ^history
• Diamond  ^history

The history of this article since it was imported to New World Encyclopedia:

• History of "Gemstone"

Note: Some restrictions may apply to use of individual images which are separately licensed.