Jasper is an opaque, impure variety of silica, usually red, yellow, brown, or green in colour, and rarely blue. Its opaque colour comes from the mineral content in the silica, such as iron or other impurities. Jasper is a form of polycrystalline quartz; like agate, it's a variety of quartz. It often contains organic material and mineral oxides, which give it interesting patterns, and it's commonly found in rounded nodules or flat bands.
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