Chapter 4 Section 4
 Most rock is igneous but it is below ground
 75 % of exposed rock is Sedimentary
 Sediments
 Rock fragments
 Mineral grains
 Bits of shell and organic matter
 Sediments pressed and cemented together or
 Minerals form from solution
 Often form in layers
 Older layers are at the bottom because they were
deposited first
 Sometimes the older layers are disrupted and moved
upward.
 Type dependent on the composition of the sediments
 They are also classified based on they way they
formed.
 3 types
 Detrital
 Chemical
 Organic
 Detrital- (dih Tri tul)
 Made from broken parts of other rocks
 Weathering- wind and water break a rock both
chemically and mechanically
 Erosion-the movement of weathered rock from place to
place.
 Compaction- erosion moves sediments to a new place
where they are deposited. Layer upon layer of sediment
builds and is pushed together by pressure
 Cementation- water moves through soil and rock and
picks up minerals. This solution of water and minerals
acts like a glue to hold the sediments together
 Dissolved minerals come out of solution
 Minerals collect when seas or lakes evaporate
 Limestone is an example
 Halite or rock salt is another example
 Remember much of the Earth was covered with water
for millions of years.
 Rocks made from the remains of once living things
 Chalk is made of microscopic remnants from shells
 Coal is formed when the dead remains of plants are
buried in swamps
 Microorganisms chemical change the plants and the
sediments are compacted for millions of years