Agates are usually translucent in thin slices, otherwise opaque. Agates occur as spherical or almond shaped inclusions in basic volcanic rock. The stripey appearance is the result of rhythmic crystallization. Under the influence of weathering a white crust forms on the outer layer and in the uppermost agate bands. Agates can be found in Brazil, Uraguay, China, India, Madagascar, Mexico, and the United States.
Many agates are normally an unattractive grey color and are only feebly patterned.
They assume their brightly colored appearance and striking structures only by being dyed. The extent to which the individual layera take on color varies according to porosity, water content, and crystallinity. There are numerous variety names depending on color and pattern. Quickly dries out in air. Patterned like the bastions of an old fortress.