Chapter 2 Section 4: Sedimentary Rocks Objectives Explain how sedimentary rocks form sediments Classify sedimentary rocks as detrital, chemical or organic in origin

Formation of Sedimentary Rocks 75% of surface rocks are sedimentary rocks Sediments: loose materials such as rock fragments, mineral grains, and bits of shell that have been moved by wind, water, ice or gravity. Sedimentary Rock Forms when sediments are pressed and cemented together or when minerals form from solutions.

Stacked Rocks Sedimentary rocks are formed with layers. Oldest layer on the bottom and the youngest is at the top

B. Classifying Sedimentary Rocks Detrital Chemical Organic Only rocks to have fossils

C. Detrital Sedimentary Rocks To wear away Made from the broken fragments of other rocks

Weathering and Erosion Weathering: Exposure to and break down (chemically and mechanically)of rock by air, water or ice Erosion: the movement of eroded sediment

2. Compaction As layers of sediment build up, pressure from upper layers on lower layers compacts lower layers into rock.

3. Cementation Large sediment needs to be cemented. Occurs when minerals are deposited between the pieces of sediments and cemented together making a detrital sedimentary rock

4. Shape and Size of Sediments Clay Silt Sand Pebbles Cobbles Boulders

5. Minerals found in Sedimentary Rocks Conglomerate usually consists of quartz and feldspar Concrete not a rock - does not occur in nature Sandstone is formed from smaller particles of conglomerates and breccias

D. Chemical Sedimentary Rocks Form when dissolved minerals come out of solution or when liquid evaporates

Limestone Calcium carbonate is carried in solution in ocean water. When it comes out of solution as calcite and it many crystals grow together limestone forms

2. Rock Salt When sea water that is rich in salt is dissolved, it often deposits the mineral halite. Halite forms rock salt

E. Organic Sedimentary Rocks Rocks made of the remains of once living things Example - limestone

Chalk Made of microscopic shells

2. Coal Forms from compacted plant remains