1. 21.3 Rocks and the Rock Cycle
Rocks are classified into three major groups based on how they formed
Igneous Rocks
Can be divided into two categories based on where they form

2. A. Intrusive Rocks – igneous rocks that form underground from magma
Cool slowly allowing crystals to grow large giving it a coarse-grain texture

3. B. Extrusive Rocks – igneous rocks that form at the surface from lava
Cool quickly resulting in the crystals to be small giving it a fine grain texture

4. Igneous Rock Textures

5. Three Main Groups of Sedimentary Rocks: 1. Clastic 2. Chemical
II. Sedimentary Rock – rock that forms over time as sediment is squeezed and cemented together
Sediment – small, solid pieces of material that comes from rocks or living organisms
Sediment is deposited in layers by running water or wind
Sediment is cemented together by pressure from overlying layers
Three Main Groups of Sedimentary Rocks:
1. Clastic
2. Chemical
3. Organic

6. Clastic Rock – sedimentary rocks that form from the broken fragments of other rocks
Clastic Rocks are classified based on the size of their fragments
Example: Conglomerate – rock fragments that consist of gravel and pebbles

7. Some clastic rocks are made of smaller particles (sandstone)

8. 2. Chemical Rocks – rocks that form when minerals precipitate out of solution
Example: when ocean water evaporates (halite)

9. Organic Rocks– rocks that form as a result of organic processes
Shells of marine animals like corals, clams, mussels sink to the ocean floor when they die.
Example: Limestone and calcite (chalk)

10. III. Metamorphic Rocks – rock that have been changed by temperature, pressure, or chemical reactions.
Most metamorphic rocks form under high temperatures and pressures deep underground. (slate and schist– shown below)

11. Metamorphic Rocks
Foliation: a layering of minerals in a rock due to intense pressure squeezing the crystals together.

12. Metamorphic Rock pictures
Metamorphic Rocks like gneiss show banding of light and dark minerals.

13. Metamorphic Rocks and their Parent Rocks
Examples:
Slate: parent is shale
Gneiss: parent is granite/schist
Quartzite: parent is sandstone
Marble: parent is limestone

14. IV. Rock Cycle
Rock Cycle – series of processes in which rocks continuously change from one type to another.