No gemstone is more creatively striped by nature than agate. This distinct and dramatically banded variety of chalcedony is composed of quartz layers. This composition varies greatly and can be of many colors. The other chalcedony family, jasper, has less-regular patterns and is less defined than the agates. Another difference between the two is that agates tend to be translucent (or at least contain translucent bands), while jaspers are generally opaque. This distinction stems from agate being composed of microscopic "fibers" of crystalline quartz while jasper is made of microscopic "grains" of crystalline quartz. Each individual agate forms by filling a cavity in a host rock. As a result, agate is often found as a round nodule with concentric bands like the rings of a tree trunk.
In ancient times, agate was highly valued as a talisman or amulet. It was said to quench thirst and protect from fever. Persian magicians used agate to divert storms. Some believed that agate would render the wearer invisible, and due to its strength and durability, it is used for making ornaments or for astrological purposes. Agate is a cooling stone and is said to cure insomnia, protect against danger, promote strength and healing, and ensure a healthy life. The major sources of agate are Australia, Canada, Mexico and the U.S.A. The gemstones of Maryland (Patuxent River Stone), Minnesota (Lake Superior agate) and South Dakota (Fairburn agate) are all agates. Find out about individual types of agate in our Gemstone Index.