Gem Encyclopedia
Diamonds are among nature’s most precious and beautiful creations.
This hardest gem of all is made of just one element: carbon. It’s valued for its colorless nature and purity. Most diamonds are primeval—over a billion years old—and form deep within the earth.
More About this Gem Buyer's GuideGIA’s Guide to Gemstones: Gem Encyclopedia
GIA’s Gem Encyclopedia is a virtual journey through the science and lore of gemstones from across the globe. Each precious stone page features additional detailed gemological information, a buyer’s guide, photos, videos & research.
Green in sunlight. Red in lamplight. Color-changing alexandrite is nature’s magic trick.
It’s the color-change variety of the mineral, chrysoberyl. Bluish green in daylight, purplish red under incandescent light; hard and durable. Top quality examples are rare and valuable.
More About this GemBuyer's Guide
Amber is nature’s time capsule. This fossilized tree resin contains remnants of life on earth millions of years ago.
Fossilized resin, color of the burnished sun--orange or golden brown. Amber might trap and preserve ancient life, including insects, leaves, even scorpions and occasionally lizards.
More About this GemBuyer's Guide
The essence of the color purple, amethyst is beautiful enough for crown jewels yet affordable enough for class rings.
Purple variety of the mineral quartz, often forms large, six-sided crystals. Fine velvety-colored gems come from African and South American mines. In demand for jewelry at all price points.
More About this GemBuyer's Guide
This transparent quartz has colors of both amethyst and citrine, and is called ametrine or amethyst-citrine.
Ametrine, one of the rarest types of transparent quartz, combines two colors: amethyst’s purple and citrine’s orange-to-yellow, growing together in a single crystal.
More About this GemBuyer's Guide
Named after seawater, aquamarine’s fresh watery hue is a cool plunge into a refreshing pool.
Blue to slightly greenish-blue variety of the mineral beryl. Crystals are sometimes big enough to cut fashioned gems of more than 100 carats. Well-formed crystals might make superb mineral specimens.
More About this GemBuyer's Guide
Citrine is the transparent, pale yellow to brownish orange variety of quartz.
Citrine’s color comes from traces of iron. It’s perhaps the most popular and frequently purchased yellow gemstone and an attractive alternative for topaz as well as for yellow sapphire.
More About this GemBuyer's Guide
Diamonds are among nature’s most precious and beautiful creations.
This hardest gem of all is made of just one element: carbon. It’s valued for its colorless nature and purity. Most diamonds are primeval—over a billion years old—and form deep within the earth.
More About this GemBuyer's Guide
Dazzling brilliance. Captivating color. The planet’s most valued gems are fancy color diamonds.
Fine color diamonds are the most rare and costly of all gemstones. Their ranks include the world’s most famous jewel—the Hope—and the most expensive gem ever auctioned—The Graff Pink.
More About this GemBuyer's Guide
Emerald is the bluish green to green variety of beryl, a mineral species that includes aquamarine.
The most valued variety of beryl, emerald was once cherished by Spanish conquistadors, Inca kings, Moguls, and pharaohs. Today, fine gems come from Africa, South America, and Central Asia.
More About this GemBuyer's Guide
Garnets are a set of closely related minerals forming a group, with gemstones in almost every color.
The garnet group of related mineral species offers gems of every hue, including fiery red pyrope, vibrant orange spessartine, and rare intense-green varieties of grossular and andradite.
More About this GemBuyer's Guide
According to legend, Vikings used iolite slices to reduce glare when checking the sun’s position.
Known in the jewelry trade as iolite, this mineral is known as cordierite to geologists and mineralogists. It was named after French mineralogist Pierre Cordier.
More About this GemBuyer's Guide
“Jade” is a generic term for nephrite, jadeite, and under certain conditions green omphacite. In China, a pierced jade disk is a symbol of heaven.
Prized by civilizations from ancient China to the Aztecs and Mayans of Central America, jade is crafted into objects of stunning artistry.
More About this GemBuyer's Guide
Collectors love kunzite for its color range, from delicate pastel pink to intense violetish purple.
Trace amounts of manganese give this pink to violet variety of spodumene its feminine glow. A relative newcomer to the gemstone stage, kunzite was only confirmed as a unique variety of spodumene in the early part of the twentieth century.
More About this GemBuyer's Guide
Lapis is a beautiful rock; an aggregate of several minerals, mainly lazurite, calcite, and pyrite.
Lapis lazuli is treasured for its beautiful deep blue color. Afghanistan is considered the source of the best-quality lapis.
More About this GemBuyer's Guide
A ghostly sheen moves under the surface of this feldspar, like moonlight glowing in water.
Feldspar prized for its billowy blue adularescence, caused by light scattering from an intergrowth of microscopic, alternating layers. Favored gem of many Art Nouveau jewelry designers.
More About this GemBuyer's Guide
Morganite is the pink to orange-pink variety of beryl, a mineral that includes emerald and aquamarine.
Like its cousins emerald and aquamarine, morganite is a variety of the beryl mineral species. This gem gets its subtle blush when a trace amount of manganese makes its way into morganite’s crystal structure.
More About this GemBuyer's Guide
Fireworks. Jellyfish. Galaxies. Lightning. Opal’s shifting play of kaleidoscopic colors is unlike any other gem.
Opal’s microscopic arrays of stacked silica spheres diffract light into a blaze of flashing colors. An opal’s color range and pattern help determine its value.
More About this GemBuyer's Guide
Perfect shining spheres. Lustrous baroque forms. Seductive strands, warm to the touch. Pearls are simply and purely organic.
Produced in the bodies of marine and freshwater mollusks naturally or cultured by people with great care. Lustrous, smooth, subtly-colored pearls are jewelry staples, especially as strands.
More About this GemBuyer's Guide
Found in lava, meteorites, and deep in the earth’s mantle, yellow-green peridot is the extreme gem
Yellow-green gem variety of the mineral olivine. Found as nodules in volcanic rock, occasionally as crystals lining veins in mountains of Myanmar and Pakistan, and occasionally inside meteorites.
More About this GemBuyer's Guide
Rose quartz is a quartz variety that gets its name from its delicate pink color.
Microscopic mineral inclusions cause the pink color and translucence of rose quartz. Well shaped, transparent pink quartz crystals are rare.
More About this GemBuyer's Guide
Ruby is the most valuable variety of the corundum mineral species, which also includes sapphire.
Traces of chromium give this red variety of the mineral corundum its rich color. Long valued by humans of many cultures. In ancient Sanskrit, ruby was called ratnaraj, or “king of precious stones.”
More About this GemBuyer's Guide
The name “sapphire” can also apply to any corundum that’s not ruby, another corundum variety.
Depending on their trace element content, sapphire varieties of the mineral corundum might be blue, yellow, green, orange, pink, purple or even show a six-rayed star if cut as a cabochon.
More About this GemBuyer's Guide
The Black Prince’s Ruby. The Timur Ruby. For centuries, spinel, the great imposter, masqueraded as ruby in Europe’s crown jewels.
Although frequently confused with ruby, spinel stands on its own merits. Available in a striking array of colors, its long history includes many famous large spinels still in existence.
More About this GemBuyer's Guide
Sunstone’s phenomenal varieties show a distinct and lively glitter called aventurescence.
Sunstone, a member of the feldspar group, can be an orthoclase feldspar or a plagioclase feldspar, depending on chemistry. Both can show aventurescence. “Sunstone” applies to the gem’s appearance.
More About this GemBuyer's Guide
Poised between lush blue, vibrant violet, and rich purple, exotic tanzanite is found in only one place on earth, near majestic Mount Kilimanjaro.
Named for Tanzania, the country where it was discovered in 1967, tanzanite is the blue-to-violet or purple variety of the mineral zoisite. It’s become one of the most popular of colored gemstones.
More About this GemBuyer's Guide
Honey yellow. Fiery orange. Cyclamen pink. Icy blue. In warm or cool tones, topaz is a lustrous and brilliant gem.
Colorless topaz treated to blue is a mass-market gem. Fine pink-to-red, purple, or orange gems are one-of-a-kind pieces. Top sources include Ouro Prêto, Brazil, and Russia's Ural Mountains.
More About this GemBuyer's Guide
Tourmalines have a variety of exciting colors with one of the widest color ranges of any gem.
Comes in many colors, including the remarkable intense violet-to-blue gems particular to Paraíba, Brazil, and similar blues from Africa. Favorite of mineral collectors.
More About this GemBuyer's Guide
Azure sky, robin’s egg blue: Vivid shades of turquoise define the color that’s named after this gem.
Ancient peoples from Egypt to Mesoamerica and China treasured this vivid blue gem. It’s a rare phosphate of copper that only forms in the earth’s most dry and barren regions.
More About this GemBuyer's Guide
Zircon is a colorful gem with high refraction and fire that’s unfairly confused with cubic zirconia.
Optical properties make it bright and lustrous. Best known for its brilliant blue hues; also comes in warm autumnal yellows and reddish browns, as well as red and green hues.
More About this GemBuyer's GuideGreen in sunlight. Red in lamplight. Color-changing alexandrite is nature’s magic trick.
It’s the color-change variety of the mineral, chrysoberyl. Bluish green in daylight, purplish red under incandescent light; hard and durable. Top quality examples are rare and valuable.
More About this GemBuyer's GuideAmber is nature’s time capsule. This fossilized tree resin contains remnants of life on earth millions of years ago.
Fossilized resin, color of the burnished sun--orange or golden brown. Amber might trap and preserve ancient life, including insects, leaves, even scorpions and occasionally lizards.
More About this GemBuyer's GuideThe essence of the color purple, amethyst is beautiful enough for crown jewels yet affordable enough for class rings.
Purple variety of the mineral quartz, often forms large, six-sided crystals. Fine velvety-colored gems come from African and South American mines. In demand for jewelry at all price points.
More About this GemBuyer's GuideThis transparent quartz has colors of both amethyst and citrine, and is called ametrine or amethyst-citrine.
Ametrine, one of the rarest types of transparent quartz, combines two colors: amethyst’s purple and citrine’s orange-to-yellow, growing together in a single crystal.
More About this GemBuyer's GuideNamed after seawater, aquamarine’s fresh watery hue is a cool plunge into a refreshing pool.
Blue to slightly greenish-blue variety of the mineral beryl. Crystals are sometimes big enough to cut fashioned gems of more than 100 carats. Well-formed crystals might make superb mineral specimens.
More About this GemBuyer's GuideCitrine is the transparent, pale yellow to brownish orange variety of quartz.
Citrine’s color comes from traces of iron. It’s perhaps the most popular and frequently purchased yellow gemstone and an attractive alternative for topaz as well as for yellow sapphire.
More About this GemBuyer's GuideDiamonds are among nature’s most precious and beautiful creations.
This hardest gem of all is made of just one element: carbon. It’s valued for its colorless nature and purity. Most diamonds are primeval—over a billion years old—and form deep within the earth.
More About this GemBuyer's GuideDazzling brilliance. Captivating color. The planet’s most valued gems are fancy color diamonds.
Fine color diamonds are the most rare and costly of all gemstones. Their ranks include the world’s most famous jewel—the Hope—and the most expensive gem ever auctioned—The Graff Pink.
More About this GemBuyer's GuideEmerald is the bluish green to green variety of beryl, a mineral species that includes aquamarine.
The most valued variety of beryl, emerald was once cherished by Spanish conquistadors, Inca kings, Moguls, and pharaohs. Today, fine gems come from Africa, South America, and Central Asia.
More About this GemBuyer's GuideGarnets are a set of closely related minerals forming a group, with gemstones in almost every color.
The garnet group of related mineral species offers gems of every hue, including fiery red pyrope, vibrant orange spessartine, and rare intense-green varieties of grossular and andradite.
More About this GemBuyer's GuideAccording to legend, Vikings used iolite slices to reduce glare when checking the sun’s position.
Known in the jewelry trade as iolite, this mineral is known as cordierite to geologists and mineralogists. It was named after French mineralogist Pierre Cordier.
More About this GemBuyer's Guide“Jade” is a generic term for nephrite, jadeite, and under certain conditions green omphacite. In China, a pierced jade disk is a symbol of heaven.
Prized by civilizations from ancient China to the Aztecs and Mayans of Central America, jade is crafted into objects of stunning artistry.
More About this GemBuyer's GuideCollectors love kunzite for its color range, from delicate pastel pink to intense violetish purple.
Trace amounts of manganese give this pink to violet variety of spodumene its feminine glow. A relative newcomer to the gemstone stage, kunzite was only confirmed as a unique variety of spodumene in the early part of the twentieth century.
More About this GemBuyer's GuideLapis is a beautiful rock; an aggregate of several minerals, mainly lazurite, calcite, and pyrite.
Lapis lazuli is treasured for its beautiful deep blue color. Afghanistan is considered the source of the best-quality lapis.
More About this GemBuyer's GuideA ghostly sheen moves under the surface of this feldspar, like moonlight glowing in water.
Feldspar prized for its billowy blue adularescence, caused by light scattering from an intergrowth of microscopic, alternating layers. Favored gem of many Art Nouveau jewelry designers.
More About this GemBuyer's GuideMorganite is the pink to orange-pink variety of beryl, a mineral that includes emerald and aquamarine.
Like its cousins emerald and aquamarine, morganite is a variety of the beryl mineral species. This gem gets its subtle blush when a trace amount of manganese makes its way into morganite’s crystal structure.
More About this GemBuyer's GuideFireworks. Jellyfish. Galaxies. Lightning. Opal’s shifting play of kaleidoscopic colors is unlike any other gem.
Opal’s microscopic arrays of stacked silica spheres diffract light into a blaze of flashing colors. An opal’s color range and pattern help determine its value.
More About this GemBuyer's GuidePerfect shining spheres. Lustrous baroque forms. Seductive strands, warm to the touch. Pearls are simply and purely organic.
Produced in the bodies of marine and freshwater mollusks naturally or cultured by people with great care. Lustrous, smooth, subtly-colored pearls are jewelry staples, especially as strands.
More About this GemBuyer's GuideFound in lava, meteorites, and deep in the earth’s mantle, yellow-green peridot is the extreme gem
Yellow-green gem variety of the mineral olivine. Found as nodules in volcanic rock, occasionally as crystals lining veins in mountains of Myanmar and Pakistan, and occasionally inside meteorites.
More About this GemBuyer's GuideRose quartz is a quartz variety that gets its name from its delicate pink color.
Microscopic mineral inclusions cause the pink color and translucence of rose quartz. Well shaped, transparent pink quartz crystals are rare.
More About this GemBuyer's GuideRuby is the most valuable variety of the corundum mineral species, which also includes sapphire.
Traces of chromium give this red variety of the mineral corundum its rich color. Long valued by humans of many cultures. In ancient Sanskrit, ruby was called ratnaraj, or “king of precious stones.”
More About this GemBuyer's GuideThe name “sapphire” can also apply to any corundum that’s not ruby, another corundum variety.
Depending on their trace element content, sapphire varieties of the mineral corundum might be blue, yellow, green, orange, pink, purple or even show a six-rayed star if cut as a cabochon.
More About this GemBuyer's GuideThe Black Prince’s Ruby. The Timur Ruby. For centuries, spinel, the great imposter, masqueraded as ruby in Europe’s crown jewels.
Although frequently confused with ruby, spinel stands on its own merits. Available in a striking array of colors, its long history includes many famous large spinels still in existence.
More About this GemBuyer's GuideSunstone’s phenomenal varieties show a distinct and lively glitter called aventurescence.
Sunstone, a member of the feldspar group, can be an orthoclase feldspar or a plagioclase feldspar, depending on chemistry. Both can show aventurescence. “Sunstone” applies to the gem’s appearance.
More About this GemBuyer's GuidePoised between lush blue, vibrant violet, and rich purple, exotic tanzanite is found in only one place on earth, near majestic Mount Kilimanjaro.
Named for Tanzania, the country where it was discovered in 1967, tanzanite is the blue-to-violet or purple variety of the mineral zoisite. It’s become one of the most popular of colored gemstones.
More About this GemBuyer's GuideHoney yellow. Fiery orange. Cyclamen pink. Icy blue. In warm or cool tones, topaz is a lustrous and brilliant gem.
Colorless topaz treated to blue is a mass-market gem. Fine pink-to-red, purple, or orange gems are one-of-a-kind pieces. Top sources include Ouro Prêto, Brazil, and Russia's Ural Mountains.
More About this GemBuyer's GuideTourmalines have a variety of exciting colors with one of the widest color ranges of any gem.
Comes in many colors, including the remarkable intense violet-to-blue gems particular to Paraíba, Brazil, and similar blues from Africa. Favorite of mineral collectors.
More About this GemBuyer's GuideAzure sky, robin’s egg blue: Vivid shades of turquoise define the color that’s named after this gem.
Ancient peoples from Egypt to Mesoamerica and China treasured this vivid blue gem. It’s a rare phosphate of copper that only forms in the earth’s most dry and barren regions.
More About this GemBuyer's GuideZircon is a colorful gem with high refraction and fire that’s unfairly confused with cubic zirconia.
Optical properties make it bright and lustrous. Best known for its brilliant blue hues; also comes in warm autumnal yellows and reddish browns, as well as red and green hues.
More About this GemBuyer's GuideYou Might Also Like
Find a Retailer
learn more
Shop the Campus Store
Learn More
Subscribe to Knowledge Rocks Emails
Learn More