Agate is a crystalized form of silica, made up primarily of chalcedony, a type of quartz that is composed of very fine intergrowths of the minerals quartz and moganite. Agates form primarily in cavities of volcanic rock by the deposition of silica from groundwater that seeps through the rocks. Gradually layers of silicate material build up eventually filling the cavity completely. The layers often have subtle differences in mineral content and impurities giving the agate a banded appearance. This banding gives many agates interesting colors and patterns that make it a popular gemstone. Sometimes these patterns resemble familiar natural scenes such as mountains, skies, rivers and trees. These agates are called “Landscape agates”.

Also see: Opal – The Most Spectacular Gemstone and Fordite or Detroit Agate

A landscape agate that resembles an ocean with low clouds on the horizon. Photo credit