Rock Topics

Origins of Sedimentary Rocks (Part 2)

Chemical Sedimentary Rocks

Chemical sedimentary rocks form from sediment particles that were inorganically precipitated from liquids.  Examples include limestone and gypsum.

Microcrystalline limestone
Microcrystalline limestone (Photograph by Parvinder Sethi)

Microcrystalline limestone is an example of an inorganically precipitated sedimentary rock.  This rock formed when water was saturated with calcium carbonate that precipitated as tiny crystals of calcite.

Organic Sedimentary Rocks

Organic sedimentary rocks form from the action of organisms.  Examples include fossiliferous limestone and coal. 

Limestone and CoalLeft: Fossiliferous limestone (Photograph by Stan Johnson); right: Coal (Photograph by Phyllis Newbill)

MapFossiliferous limestone and coal are two examples of organically-formed sedimentary rocks.  This fossiliferous limestone (left) is from Giles County, and was formed from the shells of many aquatic organisms.  This coal (right) is from Wise County, and is the remains of ancient plants.