Sedimentary Rocks

After completing this section, students will identify sedimentary rocks and explain how they

are formed (Standard PI – 024)

Sedimentary rocks are rocks that have been formed from pieces of other rock

(sediments)

Sedimentary rocks are classified by three basic

formation processes

Clastic rocks Organic rocks

Chemical rocks

Clastic Rocks – formed from fragments of other rocks

Classified by particle size and shape

Conglomerate

A cemented mix of rounded rock fragments

Breccia

Cemented rock fragments with angular (sharp) edges

Sandstone – a cemented or compacted mix of sand-sized

fragments

Fragments of rock are about the size of the head of a pin and made mostly of quartz

Shale – compacted pieces of rock the size of flour particles

Smooth, soft and easily broken

Chemical Rocks

Formed when dissolved minerals precipitate out of lake, sea or underground

water

Rock Salt

It is typically formed by the evaporation of salty water

Rock Gypsum

Gypsum rocks are sedimentary rocks made up of sulfate minerals

Limestone

Limestone is produced from the mineral calcite (calcium carbonate) and

sediment.

Organic Rocks

Organic sedimentary rocks are composed of the remains of dead organisms.

Fossiliferous Limestone

Limestone that contains large shell or coral fragments is called coquina.

Coal

Coal forms from the build up and decay of plant and animal material that has been buried under layers of sediment