Rocks and Minerals Sedimentary rocks Sedimentary rocks Form

Rocks and Minerals Sedimentary rocks

Sedimentary rocks: • • • Form from the weathering of other rocks. Form from accumulated sediments. Usually form from material that has been deposited in water. Sometimes form from wind or ice deposited sediments. Sometimes retain the characteristics of the sediments from which they form (ex. Layering).

• Sandstone in Utah

Sedimentary rocks: • Are divided into three categories: • Clastic (fragmental) • Chemical (crystalline) • Organic (bioclastic)

Clastic rocks: • Form from clastic sediment - particles of rock that have been produced by weathering and erosion

• Sediments become lithified (made into rock) in two steps. • Compaction - as layers of sediment accumulate, the bottom layers are squeezed into a denser mass

• Cementation - minerals such as calcium carbonate, iron oxide or silica in groundwater cement compacted grains together.

• • • Clastic sedimentary rocks usually form where a river or stream enters a quiet body of water. Are often stratified (layered) May contain fossils

• Clastic sedimentary rocks are classified based on the grain size of the sediment they contain (reference tables pg 6)

Chemical Sedimentary Rocks • • • Form from materials that were once dissolved in water Form when water is oversaturated with mineral ions Often form when the evaporation rate is greater than the rate that fresh water enters a body of water

Death Valley Salt Flats

• • Are often called evaporites (halite & gypsum) Are always monominerallic

Organic Sedimentary Rocks • • Form as a result of biological processes. Can form directly from plant or animal remains (coal and fossiliferous limestone. )