Gems : Agate

Agate, the gemstone for Gemini, is the most common form of a family of gemstones called Chalcedony. This includes the quartz variety (Citrine and Amethyst), and is best known for the beautiful stones often found in signet rings. Bloodstone (a green material with red flecks), Black Onyx and Cornelian are the most popular.
One of the most unusual forms is banded agate. This can be cut either across the banding, to produce stripes, or parallel, producing a layered stone which makes fascinating seal (intaglio) engraving. It can also be carved to produce rare and much-prized coloured stone cameos.
Agate can be many different colours, and is often used to make quite large decorative items. Because its banding is so variable, different agates have been given different descriptive names, such as moss agate and picture agate.