1. Classifying Rocks
SE65 c. Construct an explanation of how to classify rocks by their formation and how rocks change through geologic processes in the rock cycle

2. Classifying Rocks
Rocks are put into 3 categories based on how they form:
Igneous
Sedimentary
Metamorphic
Within those groups, rocks can be classified further by their composition and texture.

3. Composition – the minerals that make up the rock

4. Texture
Texture – the size, shape, and positions of the grains that make up a rock

5. Igneous Rocks
Igneous rock forms when hot, liquid rock, or magma, cools and solidifies (hardens)
Igneous rocks are classified by their composition and texture

6. Composition felsic mafic
Felsic – these igneous rocks are lighter in color, less dense, and are rich in aluminum, potassium, silicon, and sodium.
Mafic – these igneous rocks are darker in color, denser, and are rich in calcium, iron, and magnesium.
felsic
mafic

7. INTRUSIVE IGNEOUS ROCKS
Form when magma is cooled very slowly inside the Earth.
The surrounding material acts as an insulator to keep the magma warm.
Since the magma takes a long time to cool, the minerals have time to crystallize and grow. These rocks form large crystals.
The texture of intrusive rocks is coarse-grained since the mineral crystals are visible.

8. Granite

9. Gabbro

10. Diorite

11. Andesite

12. EXTRUSIVE IGNEOUS ROCKS
Form when lava is cooled quickly on the surface the Earth.
The air and water help cool the lava down very fast. Sometimes the lava cools so fast that air bubbles get trapped in the lava.
Since the lava cools so quickly, the minerals don’t have time to crystallize and grow. These rocks form small crystals.
The texture of extrusive rocks is fine-grained since the mineral crystals are too small to see.

13. Pumice

14. Scoria

15. Basalt

17. An easy way to remember how a sedimentary rocks is WEDCC
Sedimentary rocks make up ¾ of the Earth’s rocks
Rocks break down into sediments through weathering.
These sediments move from one place to another and are deposited in layers (strata). Over a long period of time, these layers get covered by more sediment and become compacted.
Dissolved minerals, such as calcite and quartz, act as a cement that binds the sediments together.
An easy way to remember how a sedimentary rocks is WEDCC

18. W.E.D.C.C.
W – WEATHERING (running water or wind breaks rocks into sediments)
E – EROSION (running water or wind carries away sediments)
D – DEPOSITION (sediment drops out of water or wind)
C – COMPACTION (sediments are pressed together)
C – CEMENTATION (LITHIFICATION) (sediments are glued together with dissolved minerals)

19. 3 Types of Sedimentary Rock
Clastic – made from fragments of rocks cemented together by a mineral
Classified by its fragment sizes
Fine-grained
Medium-grained
Coarse-grained

20. Conglomerate

21. Sandstone
Strata – layers of rock

22. Chemical – formed when minerals crystallize out of a solution, like water, to form a rock

23. Chert

24. Organic – formed from the remains of plants and animals
Examples include limestone and coal

25. Limestone

27. Metamorphic Rocks Metamorphism means “change shape”
Metamorphic rocks change with heat and pressure
Metamorphic rocks can change many times into other rocks

28. How does metamorphism occur?
Contact Metamorphism
Magma heats surrounding rock and changes it
Regional Metamorphism
Pressure builds up in rock that is buried below other rock formations
Pieces of Earth’s crust collide with each other

29. Textures of Metamorphic Rock
Foliated
Nonfoliated
Mineral grains are arranged in planes or bands
Mineral grains are not arranged in planes or bands
Commonly made of one or only a few minerals
The crystals change in size or composition called recrystallization

30. Gneiss

31. Schist

32. Quartzite

33. Novaculite

34. Structures
Deformation – change in shape of a rock caused by a force placed on it
Causes folds, or bends
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