1. Rocks and Minerals
4 September 2015

2. Rocks and Minerals: Definitions
A mineral is solid inorganic material of the Earth that has both a known chemical composition and a crystalline structure that is unique to that mineral
A rock is a solid aggregate of one or more minerals that have been cohesively brought together by a rock-forming process.

4. Earth Interior: Physical

5. Minerals the building blocks of rocks
Mineral Characteristics
natural
inorganic
solid
definite composition
crystal structure

6. Mineral Composition
Minerals are grouped or classified based on their composition. There are 6 groups
1. Carbonates - contain carbon, oxygen, and one ore more metallic element

7. 2. Silicates formed from silicon and oxygen
elements combined to form a silicon tetrahedron, 1 silicon atom and 4 oxygen atoms
formed from cooling magma
either near the surface (few crystals) or deep below surface (larger crystals)

8. 3. Oxides
- Minerals that contain oxygen and one or more other element(s)

9. Gypsum
4. Sulfates and Sulfides
- Minerals containing sulfur
Pyrite

10. 5. Halides
Halite
-minerals containing halogen ions plus one or more other elements

11. 6. Native Elements
Minerals that exist in a relatively pure form i.e. Gold, silver, copper
Gold crystal structure

12. Rocks Elements are chemically combined to form minerals
Minerals are physically combined to form rocks.

13. Igneous Rocks Magma- molten material underground
Lava- magma that reaches the surface
Igneous rocks are formed from magma that has cooled and hardened either beneath the surface or from a volcanic eruption

14. 2 Ways to Form Igneous Rock
Intrusive Igneous Rocks- form when magma hardens beneath Earth’s surface
Magma intrudes into existing rocks
Extrusive Igneous Rocks- form when lava hardens on the surface of the Earth
Extruded onto the surface
rhyolite
granite

15. Magma contains some gases, including water vapor- this make it less dense, so it rises
As magma rises, it cools and forms crystals
The longer the cooling time the larger the crystals

16. Granitic Composition- contain mainly quartz and feldspar, some with biotite mica and amphibole. Make up major rocks of continental crust
Basaltic Composition- contain mainly dark colored minerals and feldspar, along with Mg and Fe. Darker and denser than granitic composition

17. Igneous rock classification scheme based on mineral composition and texture. There are other blends of minerals with various textures, many of which have specific names.

18. Granite is a coarse-grained igneous rock composed mostly of light-colored, light-density, nonferromagnesian minerals. The earth's continental areas are dominated by granite and by rocks with the same mineral composition of granite.

19. This is a piece of obsidian, which has the same chemical composition as the granite. Obsidian has a different texture because it does not have crystals and is a volcanic glass. The curved fracture surface is common in noncrystalline substances such as glass.

20. Sedimentary Rocks- formed from compacted and cemented sediments
Weathering physically and chemically breaks rocks into small pieces called sediments
Sediments are moved
by wind, water, ice,
and gravity
Eventually, they are dropped and form layers that are cemented together

21. Weathering, Erosion, and Deposition
Weathering breaks rocks down
Erosion involves weather and the removal of rock
Deposition is the dropping of sediments
Sediments are deposited according to size

22. Compaction and Cementation
Compaction is the process that squeezes the water out of the sediments. It is caused by the weight of the sediments.
Cementation takes place when dissolved minerals are deposited in the tiny spaces among the sediments.
Cementing holds the sediments together.

23. Classification of Sedimentary Rocks- based on formation
Clastic Sedimentary Rocks are formed from weathered bits of rocks and minerals
Grouped according to size of the sediments in the rock
Chemical Sedimentary Rocks are formed when dissolved minerals precipitate from water solution
Coquina
limestone

24. Sedimentary rocks hold many clues to the Earth’s history
Layers of sediments are records of geologic events on Earth
Fossils are unique to sedimentary rocks

25. This is a sample of breccia, a coarse-grained sedimentary rock with coarse, angular fragments. Compare the grain sizes to the centimeter scale.

26. This is a sample of sandstone, a sedimentary rock that formed from sand grains in a matrix of very fine-grained silt, clay, or other materials. The grains in this sample are mostly the feldspar and quartz minerals, which probably accumulated near the granite from which they were eroded.

27. This is a sample of limestone, a sedimentary rock made of calcium carbonate that formed under water directly or indirectly from the actions of plants and animals. This fine-grained limestone formed indirectly from the remains of tiny marine organisms.

28. Metamorphic Rocks- form when existing rocks undergo change through heat and pressure
Metamorphism means to change
Most metamorphic changes occur at high temperatures and pressure
These occur deep below the Earth’s surface and extend into the mantle

29. Agents of Metamorphism
Heat- causes existing minerals to recrystallize or new minerals to form
Pressure- causes the spaces between mineral grains to close= more compact rock= greater density

30. Increasing metamorphic change occurs with increasing temperatures and pressures. If the melting point is reached, the change is no longer metamorphic, and igneous rocks are formed.

31. This is a sample of marble, a coarse-grained metamorphic rock with interlocking calcite crystals. The calcite crystals were recrystallized from limestone during metamorphism.

32. Rock Cycle
Earth is a dynamic planet with the surface and interior in a constant state of flux.
Internal changes alter the surface by moving the Earth’s plates, building mountains.
Seas advance and retreat over the continents brining in new materials and taking other materials away.
Rocks are continually being changed by Earth’s forces

33. A schematic diagram of the rock cycle concept, which states that geologic processes act continuously to produce new rocks from old ones.

34. The Rock Cycle

35. Planetary History
Planets formed hot: Energy from collisions, radioactivity
Heavier materials dropped to center: metals at core; basic, mafic rocks in mantle; lighter float to top (differentiation)
Radioactive heating declines; crust solidifies
Tectonics, impacts, volcanism, erosion modify surfaces (next lectures)