Polarized light micrograph of a thin section of agate microcrystals. Detail of banded agate. In the center of the image there are quartz crystals with quartz microcrystals surrounded by microscopic crystal intergrowths in multi-colored banding. The agate is a semi-precious gemstone variety of chalcedony. It is a microcrystalline silica with a chemical composition of SiO2 (silicon dioxide), and some of its other physical properties are those of quartz. Its uses are: hardstone carving, decorative arts, jewellery, crafts and industry. Field of view size: 7.1 x 10.6 mm (0.27 x 0.42 in)