1. Rocks

2. How Geologists Classify Rocks
When studying a rock sample, geologists observe the rock’s color and texture and determine its mineral composition.
Geologists can then identify a rock’s origin, or where and how it formed.

3. Texture
Most rocks are made up of particles of minerals or other rocks, called grains.
A rock’s texture is the size, shape, and pattern of the rock’s grains.
Some rocks are smooth and glassy, others are rough or chalky.

4. Grains Texture due to the grains can vary depending on the grain:
Size (fine/coarse)
Shape (rounded/jagged)
Pattern (Banded/Nonbanded)
Visible/Invisible

5. Three Major Groups of Rocks

6. Igneous Rock Any rock that forms from magma or lava.
Extrusive rock is igneous rock formed from lava that erupted onto Earth’s surface.
Example: Basalt
Intrusive rock is igneous rock that formed when magma hardened beneath the Earth’s surface.
Example: Granite

7. Igneous Rock
Igneous rocks are classified according to their origin, texture, and mineral composition.
Origin: Intrusive/Extrusive
Texture: fine/coarse grained, porphyritic, etc…
Mineral Composition: silica content

8. Sedimentary Rocks
Sedimentary rocks form from particles (sediments) deposited by water and wind.
Sediment is small, solid pieces of material that come from rocks or living things.

9. Sedimentary Rock Cycle
Sediment undergoes the following process that will change it into sedimentary rock.
1) Erosion
2) Deposition
3) Compaction
4) Cementation

10. Erosion and Deposition
Erosion occurs when running water or wind loosens and carries away fragments of rock.
Deposition is when sediment settles out of the wind or water carrying it.
After the sediments have been deposited, they begin to compact.

11. Compaction and Cementation
Compaction is the process of pressing the sediments together.
While compaction is taking place, minerals dissolve and seep in between the spaces.
Cementation occurs when the minerals crystallize and “glue” the sediment together.

12. Types of Sedimentary Rocks
There are three major groups of sedimentary rocks: Clastic, Organic, and Chemical rocks.
Clastic: Rock fragments squeezed together.
Organic: Plant and animal remains.
Chemical: Minerals dissolved in a solution crystallize.

13. Rock Examples Clastic Rocks: Shale: particles of clay
Sandstone: sand on beaches.
Conglomerate: rock fragments of different sizes.
Organic Rocks:
Coal: swamp plant remains
Limestone: made from shells.
Chemical Rocks:
Rock Salt: mineral evaporation.

14. Metamorphic Rocks
Metamorphic comes from the Greek word meta that mean “change” and morphosis that means “form”
HEAT AND PRESSURE deep beneath the Earth’s surface can change ANY rock into metamorphic rock.
Forces can push rock back toward the heat of the mantle and change rock to metamorphic rock.

15. Classifying Metamorphic Rocks
Geologists classify metamorphic rocks by the arrangement of the grains that make up the rocks.
Grains arranged in parallel layers or bands are said to be foliated.
Some metamorphic rocks are nonfoliated and the grains are arranged randomly.