Gemstones are minerals that have been, or may be, fashioned to use for personal adornment. They are beautiful, rare and durable. Organic gems come from plants and animals - and were produced by living organism. Natural Pearls, Coral, Bone, Ivory, Amber or Jet are organic materials, not stones, and are not as durable as mineral gems. The most usual method of fashioning a gem is to cut the surface into a number of flat faces, known as facets.
Agates occur in igneous rocks such as volcanic lavas.
When split open, they reveal an amazing variety of colors and patters and a banding that distinguishes agate from other kids of chalcedony. Petrified wood is fossilize wood that has had its organic matter replaced by agate. Agate is usually cut or polished for use as ornaments or pendants. Most agate now comes from huge deposits in Uruguay and Brazil. Its striking color owes its uniqueness to the amount of lead found in the compound.