Amethyst, once though to protect the wearing from getting drunk.

Pear-cut amethyst.

Trillion-cut amethyst.

An oval-cut amethyst.

Round cut amethyst.

Ametrine, a blend of amethyst and citrine.

Amethyst is the birthstone for February.  While no longer as rare as the "big three", fine amethyst used to rival sapphire, emerald, and ruby in the top of the colored gemstone world.  Purple was the color of royalty, and as such, has been used in royal crown jewels for ages, including the British coronation regalia.

Because of the purple color, amethyst was associated with the Greek god Bacchus, the god of wine.  It was said that wearing amethyst would prevent the wearer from getting drunk.  Cups carved out of amethyst were also made for this reason.

Amethyst is the purple variety of quartz.  Another popular variety of quartz is citrine, which is the yellow to orange variety.  There is also one place in the world where amethyst and citrine sometimes grow together in the same crystal, which is then called ametrine.  Quartz is a 7 on the Moh's scale of hardness.  This makes it a good stone for an occasional use ring, earrings, or a pendant.