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