Chapter 3 Section 5 How are sedimentary rocks classified? Objective: Identify and describe the two main groups of sedimentary rocks.

Key Terms clastic rock: sedimentary rock made up of fragments of rock nonclastic rock: sedimentary rock made up of dissolved minerals or the remains of living things

Groups of Sedimentary Rocks There are two groups of sedimentary rocks. One group is made up of fragments of rock that have been eroded, transported by water, wind, or ice, and deposited elsewhere. These sedimentary rocks are called clastic rocks. Another group of sedimentary rock is made up of dissolved minerals or the remains of plants and animals. These sedimentary rocks are nonclastic rocks.

DEFINE: What are clastic rocks?

Particle Size Clastic rocks can be classified according to the sizes and shapes of the sediments that formed them. Conglomerates are clastic rocks that are made up of rounded pebbles and gravel.

Particle Size Sandstones are made of small grains of sand. Shales are clastic rocks made of silt and clay. Silt and clay are the smallest kinds of sediment.

2. IDENTIFY: Name three groups of clastic rocks.

Dissolved Minerals Most nonclastic form from dissolved minerals. Rocks formed in this way are chemical rocks. When water evaporates from salty lakes and shallow seas, the salts are left behind. These salts form a mineral called halite. Rock salt is a sedimentary rock made up of halite. Some kinds of limestone also form from dissolved minerals. One dissolved mineral that forms limestone is calcite.

Dissolved Minerals Some caves have icicle-shaped deposits of limestone hanging from their ceilings. These deposits are called stalactites. The same cave may also have cone-shaped deposits of limestone rising from its floor. Deposits that rise from the floor are called stalagmites.

Dissolved Minerals Stalactites and stalagmites are formed from dipping water containing dissolved calcium carbonate. Sometimes a stalactite and stalagmite may join to form a structure called a column.

3. NAME: What mineral make up rock salt?

Plants and Animals Some nonclastics form from the remains of plants and animals. Rocks formed from the remains of living things are organic rocks. Coals are nonclastic rocks formed from the remains of plants. Coal forms when the remains of plants are compacted for a long time. Coquina and chalk are both nonclastic limestones made up of seashells.

4. DESCRIBE: How is coal formed?

Classwork CHECKING CONCEPTS Nonclastics are formed from the remains of ___ and ___. Silt and ___ are two kinds of sediment in shale. Caves often have structures called ___ hanging from their ceilings. Coal is a ___ sedimentary rock.

Classwork THINKING CRITICALLY 5. CLASSIFY: Which group of nonclastic rock is most likely to form from plants buried for a long time? 6. CLASSIFY: Which group of clastic rock might form from the largest kinds of sediment?