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