Agate

Agate is the same kind of rock as chert, but in a much purer, more transparent form. It consists of amorphous or cryptocrystalline silica, the mineral chalcedony. Agate forms from solutions of silica at relatively shallow depths and low temperatures, and is exquisitely sensitive to the physical and chemical conditions around it. It is commonly associated with the silica mineral opal. Fossilization, soil formation, and alteration of existing rock can all create agate.

Agate occurs in infinite variety and is a favorite material among lapidaries. Its fluid forms lend themselves to attractive cabochons and similar flat or rounded jewelry formats.

This stone, magnified several times, displays cracks that extend only a few millimeters from the surface. They are completely healed and do not affect the stone's strength. For a larger specimen, see the agatized tree-trunk in the Fossil Wood Gallery.

For deep geologic information on agates, including hundreds of pictures, visit the Agate Resources page from the University of Nebraska. Blue agate is Nebraska's state rock.

See more sedimentary rocks in the Sedimentary Rocks Gallery.

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