1. Chapter 4
Rocks

2. Classifying rocks Rocks are made up of two or minerals.
About 20 minerals make up most of the earth’s rocks.
When studying rocks, geologists observe the mineral composition, color and texture of the rock.
This rock contains
three minerals.

3. Rock color
A rock’s color can indicate the rock’s mineral composition. Certain minerals are light in color while other minerals are dark in color.
Granites are usually light
Basalts are usually dark

4. Rock Texture Texture involves 3 components: Grain size Grain shape
Coarse grained
Texture involves 3 components:
Grain size
Grain shape
Grain pattern
Fine grained
Jagged grains
Rounded grains
banded
Nonbanded

5. Three Groups of Rocks Igneous – form from the cooling of magma or lava
Sedimentary – form when particles of rocks are pressed & cemented together
Metamorphic – when existing rocks are changed by heat, pressure, or chemical reactions.

6. This is NOT the correct answer!

7. IGNEOUS ROCKS Granite Basalt Most common Intrusive rock
Igneous rocks are classified according to their origin, texture, and mineral composition.
ORIGIN:
Extrusive – formed from lava that has erupted.
Intrusive – formed when magma hardens under the earth’s surface.
Most common
Extrusive rock
Basalt
Most common
Intrusive rock
Granite

8. Extrusive vs. Intrusive
Rapid cooling
Small crystal size; fine grained
Can have a glassy texture
Intrusive
Slow cooling
Larger crystals; coarse grained

10. Types of Magma/Lava
Different compositions of lava or magma determine the types of igneous rocks formed.
Magma that contains SILICA will form light colored rocks such as granite.
If the magma is low in silica will form dark colored rocks such as basalt.

11. Uses of Igneous Rock
Igneous rock has been used for thousands of years for buildings and statues. Granite is the most widely used igneous rock.

12. SEDIMENTARY ROCKS
Sediments are small bits & pieces of rocks, shells, sand, bones, or parts of plants.
This is
called silt
Can you see
the shells?
Sediments can be carried
away by water to be
deposited somewhere else.

13. From Sediment to Rock Step 3 Step 4 Steps 1 & 2 Erosion Compaction
Particles are carried away by wind or water
Particles are deposited
DEPOSITION
Compaction
Particles are squeezed together by pressure
Cementation
Particles are glued together as mineral solutions harden
Step 3
Step 4
Steps 1 & 2

14. Sedimentary rock formation

16. Formation under water

17. Three Major Types of Sedimentary Rocks
Clastic
Rock formed by rock fragments that are cemented together; sometimes visible large fragments, sometimes small, fine fragments
Two common types are conglomerates, sandstone, breccias
Organic
Rocks formed by the remains of plants/animals that are cemented together.
Two common types are coal and limestone
Chemical
Formed when minerals dissolved in water are crystallized when the water evaporates away
Calcite and Halite can form this way.

18. CLASTIC SEDIMENTARY ROCKS
This is a breccia.
Notice the jagged
edges.
This is sandstone.
The individual fragments
Are not easily seen.
These are conglomerates
This is shale, splits
easily into thin sheets.

19. ORGANIC SEDIMENTARY ROCKS
Limestone – forms in the ocean from shells, corals, calcite skeletons being compacted
Coquina- a special type of limestone
In which shells can be easily seen
Coal is one of the most
important organic rocks.
Fossils are found mainly
In sedimentary rocks.

20. The formation of COAL

21. Coal is made from once living plants & animals.

22. Limestone is formed from corals, and other sea animals.
These shells and animal remains get crushed and cemented together over time to form limestone.

23. Limestone formations These are located in Vietnam.
These are called pancake rocks!

24. More limestone formations
Many cave formations are made of limestone.
Here are some hot springs in limestone.

25. Chemical Sedimentary Rocks
Gypsum and Halite are two of the most common chemical sedimentary rocks.
They can also be minerals!
They formed by dissolved chemicals crystallizing as water evaporates.
For this reason they are sometimes called EVAPORITES.

26. This is a chemical form of limestone. It is called TUFA.
This is GYPSUM in a cave in
New Mexico. Gypsum is
Calcium Sulfate. It is used
In plaster of paris, drywall,
and Cement.
This is a chemical form of limestone. It is called TUFA.

27. Coral Reefs are responsible for much of the limestone on earth.
Coral is an animal much like a sea anenome. They have tentacles and eat plankton. To protect their soft bodies they secrete a hard substance called CALCITE. When they die, these calcite shells remain.

28. Ancient Coral Reef vs. Living Coral Reef
Great Barrier Reef
Australia

29. METAMORPHIC ROCKS
Heat & pressure deep in the earth can change any rock into a metamorphic rock. They can form from igneous, sedimentary and other metamorphic rocks.
Extremely high temps and pressures deep in the earth can actually change a rocks mineral composition.

30. Two Types of Metamorphic Rocks
FOLIATED
Rocks grains are
arranged in parallel
bands or layers
Common examples:
Slate, gneiss, schist
NONFOLIATED
Grains are arranged
randomly.
Common examples:
Marble, quartzite

31. Increasing pressure causes greater foliation

32. SHALE
SLATE
SCHIST
GNEISS
SEDIMENTARY ROCK

33. With pressure, granite becomes gneiss
With pressure, granite becomes gneiss. Igneous rock is changed to a metamorphic rock.

34. Nonfoliated Metamorphic Rocks
qUARTZITE
MARBLE

35. USES OF METAMORPHIC ROCK
All MARBLE

36. World’s Largest Marble Quarry Tate, GA

37. Uses of SLATE

38. The Rock Cycle

39. The Rock Cycle
It is a series of processes in the earth’s crust, mantle and on the earth’s surface that SLOWLY change rocks from one kind to another.