Gemology

Gemstone Education A-Z

A free informational reference guide to gemstones

Alexandrite

It’s the color-change variety of the mineral, chrysoberyl. Bluish green in daylight, purplish red under incandescent light; hard and durable.

Amber

Fossilized resin, color of the burnished sun–orange or golden brown. Amber might trap and preserve ancient life, including insects.

Amethyst

Purple variety of the mineral quartz, often forms large, six-sided crystals. The birthstone for February, the name of the gem comes from a Greek word that means "not drunk."

Citrine

Citrine’s color comes from traces of iron. It’s perhaps the most popular purchased yellow gemstone and an attractive alternative for topaz and yellow sapphire.

Ametrine

Ametrine, one of the rarest types of transparent quartz, combines two colors: amethyst’s purple and citrine’s orange-to-yellow.

Aquamarine

Blue to slightly greenish-blue variety of the mineral beryl. Crystals are sometimes big enough to cut fashioned gems of more than 100 carats.

Diamond

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.

Fancy Color Diamond

Only one in every 10,000 diamonds possesses natural color and is referred to as a fancy color diamond. They are purchased almost exclusively for the intensity and distribution of the diamond's color.

Emerald

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.

Garnet

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.

Iolite

Known in the jewelry trade as iolite, this mineral is known as cordierite to geologists and mineralogists. Iolite is strongly trichroic, meaning that it shows three colors when viewed from different angles.

Jade

Prized by civilizations from ancient China to the Aztecs and Mayans of Central America, jade is crafted into objects of stunning artistry. Beauty and wide-ranging expressiveness.

Kunzite

Trace amounts of manganese give this pink to violet variety of spodumene its feminine glow. Kunzite was only confirmed as a unique variety of spodumene in the early part of the twentieth century.

Lapis Lazuli

Lapis lazuli is a gemstone of the kind that might have come straight out of the Arabian Nights: a deep blue with golden inclusions of pyrites which shimmer like little stars. Stone of friendship and truth.

Moonstone

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.

Morganite

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.

Opal

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. Legend says that it is especially good for the eyes.

Pearl

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.

Peridot

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.

Rose Quartz

Microscopic mineral inclusions cause the pink color and translucence of rose quartz. Well shaped, transparent pink quartz crystals are rare. An irresistible addition to your jewelry wardrobe.

Ruby

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.”

Tanzanite

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.

Topaz

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.

Tourmaline

Tourmaline's name comes from the Sinhalese word "turmali", which means "mixed". Occurring in more colors or combinations of colors than any other gemstone, tourmaline lives up to its name.

Turquoise

It is rare and valuable in finer grades and has been prized as a gem and ornamental stone for thousands of years owing to its unique hue. The turquoise occurs as vein or seam fillings, and as compact nuggets; these are mostly small in size.

Zircon

Colorless zircon is known for its brilliance and flashes of multicolored light, called fire. These zircon properties are close enough to the properties of diamond to account for centuries of confusion between the two gems.

Peridot

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.

Opal

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. Legend says that it is especially good for the eyes.

Pearl

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.