3.5 Notes
How are sedimentary rocks classified?
Objective: Identify and describe the two main groups of sedimentary rocks
Clastic rocks are sedimentary rocks made up of fragments of rock.
Nonclastic rocks are sedimentary rocks made up of dissolved minerals or the remains of living things.
What are clastic rocks?
Clastic rocks can be classified by the sizes and shapes of the sediments that formed them.
Conglomerates are clastic rocks that are made up of pebbles and gravel. Sandstones and shales are clastic rocks made from sand, silt or clay. Silt and clay are the smallest sediments.
Name three groups of clastic rocks.
Non-clastic rocks form from dissolved minerals. These are chemical rocks. When water evaporates from salty lakes and shallow seas, the salts are left behind. Calcite dissolves to form limestone and halite dissolves to form rock salt.
Some caves have icicle-shaped deposits of limestone hanging from their ceilings.
Stalactites hang from cave ceilings.
Cone shaped deposits also rise from the floor in some caves. Stalagmites are limestone deposits rising from the floor in caves.
These deposits are formed from dripping water containing calcium carbonate.

Stalactites and stalagmites might meet to form a column.
What mineral makes up rock salt?
Nonclastic rocks can form from the remains of plants and animals. Coal is formed from the remains of plants. Coal forms when the remains of plants are compacted for a long time.
Coquina and chalk are Nonclastic limestones made up of seashells.
How is coal formed?