This is a very rare stone noted for its color changing abilities. Colors are greenish outdoors, and reddish to violet under artificial light. Alexandrite is one of the birthstones for June.

A quartz gemstone, amethyst ranges in color from clear purple to bluish violet. Birthstone for February. Legendary powers: brings luck, ensures constancy, protects against magic.

The aquamarine is part of the beryl group, as does emerald and beryl. The name means "water of the sea" because of the usual color, typically from light blue to sea green. Birthstone for March.

A cut black sapphire with a 6 rayed star. These stones are always heat treated to improve their color.

A cut blue sapphire displaying a 3 rayed, 6 point star.

A topaz ranging in color from pale blue to bright blue. Most blue topaz is irradiated & heat treated to produce their blue color. Birthstone for December.

Chatoyancy is a phenomenon seen in various gems when they are cabochon cut, resulting in a bright single line down the center.

These deep royal blue sapphires from Sri Lanka, formally Ceylon, are the finest in the world.

A semi-precious quartz gemstone, ranging in color from a light yellow to a brilliant orange.

An extremely valued gem composed of pure carbon, the hardest of all known natural substances. Birthstone for April.

Belongs to the beryl group. One of the most valuable gems, ranging in color from green to bluish-green. Birthstone for May.

A group of semi-precious stones ranging in all colors but blue. The most common color is a deep red. Birthstone for January.

The material obtained from the inside of the shell of a certain large mollusk.

A quartz mineral (chalcedony) that is usually black. Onyx was an ancient talisman used against depression.

Some of the most stunning of the semi-precious stones: luminous and iridescent. Birthstone for October.

Organic gems of calcium carbonate grown within mollusks-- specifically oysters, although in very rare cases, snails have produced pearls. Colors range from white, cream, golden, pink, silver green, blue and black. The color is determined by the type of mollusk and the water it is in. Birthstone for June.

Formerly called "chrysolite," peridot is a yellow-green semi-precious stone. During the Middle Ages, it was used for ecclesiastical purposes. Birthstone for August.

A member of the garnet group, the color ranges from rose-red or pale violet.

The hardest (and most expensive) mineral after diamond, the ruby's color ranges from deep red to pink and into brown shades. Birthstone for the month of July.

Almost as hard as diamond, sapphires are very similar to rubies, except of course in color. Birthstone for September.

Mineralogists refer to tanzanite as blue zoisite. Gorgeous color enhanced by heating. A valuable transparent blue-purple stone, tanzanite's electrifying color is enhanced by heating.

Topaz has a wide color range – historically named all yellow and brown gemstones. The most valuable color is pink. Birthstone for November.

No gemstone has such richness in color variation. One-color tourmalines are rare. Most crystals have various shades. The pink to reddish color tourmaline is one of the birthstones for October.