Ch. 6 Sec. 2 Types of Sedimentary Rocks
Sedimentary rocks are classified by their mode of formation. Review Vocabulary saturated: the maximum possible content of dissolved minerals in solution
Page 142 sandstone siltstone shale micrite coquina chalk coal dolostone flint rock qypsum rock salt
I. Clastic Sedimentary Rocks The most common sedimentary rocks, clastic sedimentary rocks, are formed from the abundant deposits of loose sediments that accumulate on Earth’s surface.
Clastic refers to rock and mineral fragments produced by weathering and erosion. These rocks are further classified according to the sizes of their particles.
A. Coarse-grained rocks Conglomerates have rounded, gravel-sized particles. a. High transport energy b. High abrasion & rounding 2. Breccias are composed of angular, gravel-sized particles.
B. Medium-grained rocks Sedimentary rocks that contain sand-sized rock and mineral fragments.
1. Sandstone a. Porosity is the percentage of open spaces between grains in a material, such as rock. b. Fluids can move through porous rock. c. Reservoirs of oil, natural gas, and groundwater.
C. Fine-grained rocks • silt- and clay-sized particles • low porosity • barriers hinder the movement of groundwater and oil.
II. Chemical and Biochemical Sedimentary Rocks involves the processes of evaporation and precipitation of minerals.
A. Chemical sedimentary rocks crystal grains precipitate out of saturated solution settle to the bottom evaporites
Types of Sedimentary Rocks The constant evaporation from a body of salt water results in precipitation of large amounts of salts.
B. Biochemical sedimentary rocks Biochemical sedimentary rocks are formed from the remains of once- living organisms. The most abundant of this type of rock is limestone, which is composed primarily of calcite.
Limestone a. Organisms with calcium carbonate shells (calcite) b. Shells settle to the bottom c. Layers of carbonate sediment d. Burial and lithification e. May contain fossils
2. Chert Contains silica shells Siliceous ooze
3. Coal Plant remains Some plant fossils
answer:Biochemical rocks form from the remains of living organisms. Examples include coal, which forms from plant remains, and chalk, which forms from microscopic fossils. Chemical rocks are direct precipitates from water. Rock gypsum is a common example.