Gemstones A to Z

A group of minerals that come in many colors. Garnet is the January birthstone.

Purple quartz, the February birthstone. Quartz is the second most abundant material in the Earth's crust.

A member of the beryl family, which also includes emerald and morganite.

A dark green chalcedony (a quartz) with red spots of iron oxide. Also called heliotrope or blood jasper.

The hardest known natural material, made of a single element, carbon. Only another diamond can scratch it.

A green variety of the mineral beryl, colored by chromium and vanadium. One of the "big four" gems with diamond, ruby and sapphire.

An organic gem formed inside a mollusk as layers of nacre build up around an irritant. Pearls are not mined or cut, and most are cultured with human help.

A rare variety of chrysoberyl that changes color with the light: "emerald by day, ruby by night".

A feldspar gem known for adularescence, a floating glow that moves as you turn it.

The red variety of the mineral corundum, colored by chromium. One of the most durable gems.

A gem form of the mineral olivine, one of the few gems found in only one color family: green.

A hard, durable gem that is often mistaken for ruby or pink sapphire. Added as an August birthstone in 2016.

A banded chalcedony quartz with alternating layers of sard and onyx, used for jewelry, seals and cameos.

A variety of the mineral corundum (the same mineral as ruby), known for its hardness and its wide range of colors.

A gem whose play of color comes from tiny silica spheres that diffract light. Opals with this effect are called precious opals. Opal holds 3 to 21 percent water.

A family of related minerals that comes in more colors than almost any other gem. It can become electrically charged when heated or squeezed.

A hard gem (8 on the Mohs scale) whose perfect cleavage makes it prone to chipping or cracking.

Yellow to golden orange quartz, colored by traces of iron. Most citrine sold is heat treated amethyst or smoky quartz.

A soft, opaque blue to green gem colored by copper (blue) and iron or chromium (green).

The blue violet variety of the mineral zoisite, found only in Tanzania near Mount Kilimanjaro. It was discovered in 1967.

A natural gem, not to be confused with man-made cubic zirconia. AGS calls it the oldest mineral on Earth: Australian zircons are about 4.4 billion years old.