1. Chapter 4: section 4

2.  Igneous rocks are the most common rocks. However, these rocks mostly exist underneath the surface of the Earth.

3.  They come from already existing rocks.  Sedimentary rocks form when sediments are pressed and cemented together, or when minerals form from solutions.

4.  Sedimentary rocks often form as stacked layers.  The older layers are at the bottom and the newest layers are on top of an undisturbed stack.

5.  To classify a sedimentary rock, determine its composition and texture.  Sedimentary rocks can be made out of any material in nature.  Sedimentary rocks are classified as:  Detrital  Chemical  Organic

6.  Detrital – “to wear away”  They are made from broken fragments of other rocks.  The loose sediments are compacted and cemented together to form solid rock.  They are named according to shape or size.  Conglomerate – rounded sediments  Breccia – sediments with sharp angles

7. - Weathering - Erosion - Compaction - Cementation

8.  Weathering – breaks rocks into smaller pieces when a rock is exposed to air, water, or ice.  Erosion is the movement of weathered material.

9. - Erosion moves sediments to a new location where they are then deposited. - Layer upon layer of sediments will build up. - Pressure from the upper layers will push down on the lower layers. - If the sediments are small, they will stick together and form solid rock in the process of compaction.

10.  If sediments are large, pressure alone can’t make them stick together.  These large sediments must be cemented together.  Cementation occurs when minerals such as quartz, calcite, and hematite are deposited between the pieces of sediment.

11.  Chemical sedimentary rocks form when dissolved minerals come out of a solution or when liquid evaporates.  You may see salt deposits at the bottom of a glass when salt water evaporates.

12.  Rocks made of the remains of once living things are called organic sedimentary rocks.  Example:  Shells - Help form fossil-rich limestone.  Chalk – shells  Coal – When dead plants are buried under other sediments in swamps.  If a rock is made completely out of shell fragments, the rock is called coquina.