Types of Sedimentary Rocks Chapter 6.2
Feb 23, 2016
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