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Silk Agate - Agate is is a microcrystalline variety of silica, chiefly chalcedony. Agate is the most common variety of chalcedony which is a form of quartz. Agate is identical with quartz in composition and physical properties. Composed of silicon dioxide (SiO2), it has a hardness of 7, a glassy luster, a conchoidal fracture, and a specific gravity of 2.60. Silk Agate forms in the oyster shell shape shown below. Although agates may be found in various kinds of rock, they are classically associated with volcanic rocks.(source: Wikipedia) Return to List Back to Michael's Hobbies page Back to Michael Marcotte's HomePage