It is perhaps surprising to learn that some minerals and rock formations are formed by living organisms themselves or from the remains of dead organisms. Furthermore, living processes can lead to the alteration of rocks. Processes, both biotic and abiotic , that lead to the formation of minerals and rocks will be further explained in lecture. Examine the following examples of rocks formed by living processes. The formation of tufa can be physical, but can be facilitated by aquatic photosynthetic activity that removes CO 2 from water.
Limestone is one of the very common sedimentary rocks comprising the upper crust of the earth .
Diatomaceous earth . In some regions can form extensive beds. Also known as flint, chert is a very hard, easily fractured rock composed of microscopic SiO 2 crystals. Chalk deposits, such as the White Cliff of Dover are the accumulated remains of marine organisms known as Foraminiferans , tiny, shelled organisms related somewhat to Amebas. Overall the process is favored in anoxic environments.