CLASSIFYING SEDIMENTARY ROCKS

Sedimentary rocks form at the Earth’s surface. Geologists divide sedimentary rocks into two major types, based on what they are made of and how they form. Clastic sedimentary rocks are composed of pieces of rock, minerals, or fossils that have been cemented together. Sandstone is an example. Chemical sedimentary rocks form by precipitation or the growth of new minerals in water. Precipitation can create large sedimentary structures like stalactites and stalagmites, which grow in caves.

The formation of both types of sedimentary rocks begins with the weathering of any igneous, sedimentary, or metamorphic rock at the Earth’s surface. Physical weathering processes break rocks down into pieces or sediments. Chemical weathering dissolves minerals in the rocks and them precipitates them.

Mt. Brockman, Australia (sandstone)

 
Stalactites and stalagmites