Dendritic agate unicorn Crystal carving

Agate is a rock consisting primarily of crypto crystalline silica, chiefly chalcedony, alternating with micro granular quartz. Agate is a translucent variety of microcrystalline quartz. It is used as a semiprecious stone when it is of desirable quality and color. Agate generally forms by the deposition of silica from groundwater in the cavities of igneous rocks. These structures produce the banded patterns that are characteristic of many agates. Agate occurs in a wide range of colors, which include brown, white, red, gray, pink, black, and yellow. The colors are caused by impurities and occur as alternating bands within the agate. Agates develop as secondary deposits in hollow cavities, called vesicles. Although they can form in all types of host rock, most of the world's agates developed in ancient volcanic lava. ... Later, these gases escaped through cracks that formed as the igneous rock cooled and hardened, leaving hollow cavities.See silica mineral (table). Agate is found throughout the world. In the United States it is produced in several western states; Oregon, Washington, Idaho, and Montana are the chief sources of gemstones. Most agates occur in cavities in eruptive rocks or ancient lavas. Our Beautiful Stones and Crystals come in different shapes, sizes, and colors.