Polarized light photomicrograph of a thin section of brazilian Agat, where thin layesrs of opaque matter mimick a tree. For its variety and distribution of colors agate is extremely beautiful also when seen with the naked eye, and valued since the antiquity. Like the more common quartz, it is made of silica (SiO2), but in a microcrystalline variety called chalcedony. Width of view ranging about 1.5 mm