22 - Chert

Hello friends, Welcome to the Rock Repository at the Department of Geology, Shivaji Science College, Nagpur.

I am chert, a hard, fine grained, biochemical sedimentary rock composed of microcrystalline or cryptocrystalline quartz. I occur in a wide variety of colors such as white, black, green, yellow, orange and red. The darker colors often result from inclusions of mineral and organic matter. I occur as nodules, concretionary masses and as layered deposits. I am also found as hot spring deposits and banded iron formations. Some varieties of me are also formed due to the replacement of calcrete in fossil soils by silica dissolved from overlying volcanic ash. Because of my weathering resistant nature, I am an ideal rock for preservation of early life forms. I am very hard with a hardness of seven on the Mohs scale of hardness and I exhibit conchoidal fracture. My most important use is in constructions and for road surfacing. I am also used to make sharp weapons such as knives and spears. Thank you for visiting.