1. How Rocks are Formed: Sedimentary
Most of Earth’s crust is made of igneous rock, but most of its surface is covered by sedimentary rocks.

2. Three Main Kinds of Sedimentary Rock
Clastic: fragments of other rocks
Chemical: mineral grains that come from dissolved solutions by evaporation or chemical action
Organic: remains of plants and animals

3. Clastic Rocks
Clastic sedimentary rocks come from the weathering of rocks that already exist
Winds, waves, and glaciers pick up and move the particles
Sediments are deposited when a stream slows down
Ocean water, lake water, and groundwater contain natural cements that include silica(SiO2), calcite (CaCO3), and iron oxide(FeO)
These dissolved minerals settle into the spaces between the sand grains or pebbles, binding them together into rock
The pressure of overlying sediments can also make fine sediments stick together

4. Clastic Rocks
Sandstone
Conglomerate
Shale

5. Chemical Sedimentary Rocks
Dissolved minerals fall out of solution
Evaporation or the combining of dissolved ions to form new minerals.
The most common are limestone, rock salt, and rock gypsum
Limestones are formed from tiny grains of calcite
Rock salt is the natural form of table salt, it is almost pure halite
Rock gypsum occurs in layers and is almost pure gypsum

6. Chemical Sedimentary Rocks
Rock Salt
Limestone

7. Organic Sedimentary Rocks
Organic sediments come from the remains of animals and plants
The most common are limestone and coal
Organic limestone is mostly calcite, shell producing animals die and their shells pile up and are cemented
Coal

8. Stratification
Stratification is the arrangement of rocks in visible layers
When there is a change in the type of sediments being laid down, new rock layers are formed
The layers are called beds and are separated by bedding planes
Cross-bedding may develop when beds are deposited by wind on dunes or by rivers on deltas or sandbars

9. Fossils in Sedimentary Rocks
Animals and plants that die as sediments pile up are buried
The hard parts may remain as fossils when the sediments turn to rock
Fossils are the remains, impressions, or any other evidence of plants and animals preserved in rock

10. Ripple Marks and Mud Cracks
Many sandstones show ripple marks that are formed by the action of winds, streams, waves or currents on sand.
Mud cracks develop when deposits of wet clay dry and contract
Mud cracks are later filled with different materials, and the clay becomes shale rock.

11. Nodules,Concretions, Geodes
Nodules are lumps of fine-grained silica called chert in limestones
Concretions are round masses of calcium carbonate in shale
Geodes are limestones with hollow spheres of silica rock, the hollows can be filled with crystals of quartz or calcite
Nodule