Gem Encyclopaedia
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 Stone Buyer's GuideGIA’s Guide to Gemstones: Gem Encyclopaedia
GIA’s Gem Encyclopaedia is a virtual journey through the science and lore of gemstones from across the globe. Each precious stone page features additional detailed gemmological information, a buyer’s guide, photos, videos & research.
Green in sunlight. Red in lamplight. Colour-changing alexandrite is nature’s magic trick.
It’s the colour-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.
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Amber is nature’s time capsule. This fossilised tree resin contains remnants of life on earth millions of years ago.
Fossilised resin, colour of the burnished sun – orange or golden brown. Amber might trap and preserve ancient life, including insects, leaves and even scorpions and occasionally lizards.
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The essence of the colour purple, amethyst is beautiful enough for crown jewels yet affordable enough for engagement rings.
Purple variety of the mineral quartz, often forms large, six-sided crystals. Fine velvety coloured gems come from African and South American mines. In demand for jewellery at all price points.
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This transparent quartz has colours of both amethyst and citrine, and is called ametrine or amethyst-citrine.
Ametrine, one of the rarest types of transparent quartz, combines two colours: amethyst’s purple and citrine’s orange-to-yellow, growing together in a single crystal.
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Named after seawater, aquamarine’s fresh watery hue is like 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.
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Citrine is the transparent, pale yellow to brownish orange variety of quartz.
Citrine’s colour comes from traces of iron. It’s perhaps the most popular and frequently purchased yellow gemstone and an attractive alternative to topaz as well as to yellow sapphire.
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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 colourless nature and purity. Most diamonds are primeval – over a billion years old – and are formed deep within the earth.
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Dazzling brilliance. Captivating colour. The planet’s most valued gems are fancy colour diamonds.
Fine colour 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.
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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.
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Garnets are a set of closely related minerals that form a group with gemstones in almost every colour.
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.
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According to legend, Vikings used iolite slices to reduce glare when checking the sun’s position.
Known in the jewellery trade as iolite, this mineral is known as cordierite to geologists and mineralogists. It was named after French mineralogist Pierre Cordier.
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Jade is actually two separate gems: nephrite and jadeite. In China, a pierced jade disc is a symbol of heaven.
Prized by civilisations from ancient China to the Aztecs and Mayans of Central America, jade is crafted into objects of stunning artistry.
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Collectors love kunzite for its colour 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.
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Lapis is a beautiful rock; an aggregate of several minerals, mainly lazurite, calcite, and pyrite.
Lapis lazuli is treasured for its beautiful deep blue colour. Afghanistan is considered the source of the best-quality lapis.
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A ghostly sheen moves under the surface of this feldspar, like moonlight glowing in water.
Feldspar is prized for its billowy blue adularescence, caused by light scattering from an intergrowth of microscopic, alternating layers. It is the favoured gem of many Art Nouveau jewellery designers.
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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.
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Fireworks. Jellyfish. Galaxies. Lightning. Opal’s shifting play of kaleidoscopic colours is unlike any other gem.
Opal’s microscopic arrays of stacked silica spheres diffract light into a blaze of flashing colours. An opal’s colour range and pattern help determine its value.
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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 molluscs naturally or cultured by people with great care. Lustrous, smooth, subtly coloured pearls are jewellery staples, especially when worn as strands.
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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.
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Rose quartz is a quartz variety that gets its name from its delicate pink colour.
Microscopic mineral inclusions cause the pink colour and translucence of rose quartz. Well shaped, transparent pink quartz crystals are rare.
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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 colour. Long-valued by humans from many cultures. In ancient Sanskrit, ruby was called ratnaraj, or “king of precious stones”.
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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 StoneBuyer'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 colours, its long history includes many famous large spinels still in existence.
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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.
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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 coloured gemstones.
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Honey yellow. Fiery orange. Cyclamen pink. Icy blue. In warm or cool tones, topaz is a lustrous and brilliant gem.
Colourless 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.
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Tourmalines have a variety of exciting colours with one of the widest colour ranges of any gem.
This stone comes in many colours, including the remarkable intense violet-to-blue gems particular to Paraíba, Brazil, and similar blues from Africa. It is a favourite of mineral collectors.
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Azure sky, robin’s egg blue – vivid shades of turquoise define the colour 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.
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Zircon is a colourful 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, it also comes in warm autumnal yellows and reddish browns, as well as red and green hues.
More about this StoneBuyer's GuideGreen in sunlight. Red in lamplight. Colour-changing alexandrite is nature’s magic trick.
It’s the colour-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 StoneBuyer's GuideAmber is nature’s time capsule. This fossilised tree resin contains remnants of life on earth millions of years ago.
Fossilised resin, colour of the burnished sun – orange or golden brown. Amber might trap and preserve ancient life, including insects, leaves and even scorpions and occasionally lizards.
More about this StoneBuyer's GuideThe essence of the colour purple, amethyst is beautiful enough for crown jewels yet affordable enough for engagement rings.
Purple variety of the mineral quartz, often forms large, six-sided crystals. Fine velvety coloured gems come from African and South American mines. In demand for jewellery at all price points.
More about this StoneBuyer's GuideThis transparent quartz has colours of both amethyst and citrine, and is called ametrine or amethyst-citrine.
Ametrine, one of the rarest types of transparent quartz, combines two colours: amethyst’s purple and citrine’s orange-to-yellow, growing together in a single crystal.
More about this StoneBuyer's GuideNamed after seawater, aquamarine’s fresh watery hue is like 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 StoneBuyer's GuideCitrine is the transparent, pale yellow to brownish orange variety of quartz.
Citrine’s colour comes from traces of iron. It’s perhaps the most popular and frequently purchased yellow gemstone and an attractive alternative to topaz as well as to yellow sapphire.
More about this StoneBuyer'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 colourless nature and purity. Most diamonds are primeval – over a billion years old – and are formed deep within the earth.
More about this StoneBuyer's GuideDazzling brilliance. Captivating colour. The planet’s most valued gems are fancy colour diamonds.
Fine colour 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 StoneBuyer'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 StoneBuyer's GuideGarnets are a set of closely related minerals that form a group with gemstones in almost every colour.
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 StoneBuyer's GuideAccording to legend, Vikings used iolite slices to reduce glare when checking the sun’s position.
Known in the jewellery trade as iolite, this mineral is known as cordierite to geologists and mineralogists. It was named after French mineralogist Pierre Cordier.
More about this StoneBuyer's GuideJade is actually two separate gems: nephrite and jadeite. In China, a pierced jade disc is a symbol of heaven.
Prized by civilisations from ancient China to the Aztecs and Mayans of Central America, jade is crafted into objects of stunning artistry.
More about this StoneBuyer's GuideCollectors love kunzite for its colour 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 StoneBuyer'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 colour. Afghanistan is considered the source of the best-quality lapis.
More about this StoneBuyer's GuideA ghostly sheen moves under the surface of this feldspar, like moonlight glowing in water.
Feldspar is prized for its billowy blue adularescence, caused by light scattering from an intergrowth of microscopic, alternating layers. It is the favoured gem of many Art Nouveau jewellery designers.
More about this StoneBuyer'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 StoneBuyer's GuideFireworks. Jellyfish. Galaxies. Lightning. Opal’s shifting play of kaleidoscopic colours is unlike any other gem.
Opal’s microscopic arrays of stacked silica spheres diffract light into a blaze of flashing colours. An opal’s colour range and pattern help determine its value.
More about this StoneBuyer'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 molluscs naturally or cultured by people with great care. Lustrous, smooth, subtly coloured pearls are jewellery staples, especially when worn as strands.
More about this StoneBuyer'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 StoneBuyer's GuideRose quartz is a quartz variety that gets its name from its delicate pink colour.
Microscopic mineral inclusions cause the pink colour and translucence of rose quartz. Well shaped, transparent pink quartz crystals are rare.
More about this StoneBuyer'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 colour. Long-valued by humans from many cultures. In ancient Sanskrit, ruby was called ratnaraj, or “king of precious stones”.
More about this StoneBuyer'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 StoneBuyer'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 colours, its long history includes many famous large spinels still in existence.
More about this StoneBuyer'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 StoneBuyer'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 coloured gemstones.
More about this StoneBuyer's GuideHoney yellow. Fiery orange. Cyclamen pink. Icy blue. In warm or cool tones, topaz is a lustrous and brilliant gem.
Colourless 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 StoneBuyer's GuideTourmalines have a variety of exciting colours with one of the widest colour ranges of any gem.
This stone comes in many colours, including the remarkable intense violet-to-blue gems particular to Paraíba, Brazil, and similar blues from Africa. It is a favourite of mineral collectors.
More about this StoneBuyer's GuideAzure sky, robin’s egg blue – vivid shades of turquoise define the colour 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 StoneBuyer's GuideZircon is a colourful 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, it also comes in warm autumnal yellows and reddish browns, as well as red and green hues.
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