Types of Sedimentary Rocks

Types of Sedimentary RocksChapter 6.2

Classifications

• Sedimentary rocks are classified by their mode of formation

• Clastic• Chemical • Biochemical

Clastic Sedimentary Rocks

• Classified according to size of their particles– Coarse grained rocks– Medium grained rocks– Fine grained rocks

Coarse grained rocks

• Gravel sized rock and mineral fragments

Conglomerates

rock

Medium grained rocks

• Sand sized rocks• Sandstone – Ripple marks and cross-bedding help geologists

map out ancient rivers – Quartz and rock fragments– High porosity

Sandstone

rock

Fine-grained rocks

• Consist of silt and clay sized particles• Siltstone and shale• Environments like swamps and ponds– Still or slow moving – Accumulate in thin horizontal layers

• Low porosity– Form barriers that hinder the movement of

groundwater and oil

Siltstone and Shale

rock

Chemical Sedimentary Rocks

• Involves the processes of evaporation and precipitation of minerals– Evaporation• Minerals are left behind• Arid areas – high evaporation rates can increase

concentration of dissolved minerals in bodies of water– Great Salt Lake– -common in arid regions

Water Cycle

Evaporates

Biochemical

• Formed from the remains of once living organisms– Limestone• Primarily calcite• Common in shallow water

– Around coral reefs• May include fossils

– Siliceous ooze solidifies– Coal

Limestone

rock

Chert

• Fine grained quartz

Conglomerate

Sandstone

Shale

Shell limestone

Coal

Calcareous tufa

• Calcite

Rock salt