1. Rocks
Section 1
The Rock Cycle

2. Three categories of rock:
Rocks
A rock is a coherent aggregate of minerals - a physical mixture.
Three categories of rock:
Igneous
Formed from cooling and crystallization of magma or lava
Sedimentary
Formed from preexisting rocks subjected to weathering and erosion
Metamorphic
Formed from preexisting rock transformed by heat, pressure, or chemical fluids 2

3. The Rock Cycle—model showing processes that create and change rock
Rock—a mixture of minerals, volcanic glass, organic matter, or other material
The Rock Cycle—model showing processes that create and change rock
Sedimentary rock can be changed by heat and pressure into metamorphic rock
Metamorphic rock can melt and cool to form igneous rock
Igneous rock can be broken into fragments that may later form sedimentary rock

4. Rock Cycle 4

5. Conservation of matter—rock cycle never destroys elements of rocks but merely redistributes them
James Hutton recognized the rock cycle in 1788 by observing Siccar Point, Scotland

6. Rocks
Section 2
Igneous Rocks

7. Igneous rocks form from magma found deep under Earth’s surface.
Magma reaching the surface flows from a volcano as lava
Magma trapped below the surface forms large-grained intrusive igneous rock when it cools.
Magma cooling at or near Earth’s surface forms small-grained extrusive igneous rock

8. Magma to Igneous Rock
The mineral makeup of igneous rock is dependent on the chemical composition of the magma from which it crystallizes.
Three types of magma:
Basaltic
Andesitic
Granitic 8

9. Basaltic igneous rocks are dark-colored and dense.
Contain iron and magnesium but very little silica
Basaltic lava flows freely from a volcano
Granitic igneous rocks are lower density and lighter color.
Contain more silica and less iron and magnesium
Granitic magma is thick and stiff

10. Andesitic rocks have a more balanced composition of minerals and density than basaltic or granitic rocks.
Crystal size, large or small, can help identify an igneous rock as intrusive or extrusive
Volcanic glass rocks cool so quickly that few crystals form
Some rocks have holes formed around once-trapped air and other gases

11. Igneous Rocks Are Classified by Their Texture
Rate of cooling determines crystal size:
Slow rate promotes the growth of fewer but larger crystals (coarse-grained).
Fast rate forms many small crystals (fine-grained).
Very fast rate forms glass (i.e., no crystals). 11

12. Section 3 Metamorphic Rocks

13. Metamorphic Rocks produced from: Igneous rocks Sedimentary rocks
Other metamorphic rocks
Metamorphism is “changed rock”; the transition of one rock into another by temperatures or pressures different from those in which it formed. 13

14. Metamorphic rocks—changed by temperature, pressure, and hot fluids
Heat and pressure result from one layer of rock on top of another layer.
Sometimes temperature and pressure are great enough to melt rock, forming magma
Sometimes pressure flattens mineral grains in rocks without melting them

15. Agents of Metamorphism
Heat is the most important agent.
Recrystallization results in new, stable minerals
Two sources of heat:
Heat from magma (contact metamorphism)
An increase in temperature with depth due to the geothermal gradient (burial metamorphism) 15

16. Agents of Metamorphism
Pressure (stress):
Increases with depth
Confining pressure applies forces equally in all directions
Rocks may also be subjected to differential stress—unequal stress in different directions
Leads to foliation 16

17. Hot, water-rich fluids can move through rock, chemically changing it.
As pressure and temperature continue to increase over time, one type of rock can change into several different metamorphic rocks.
Hot, water-rich fluids can move through rock, chemically changing it.
Classification of metaphoric rocks—by composition and texture
Foliated texture – minerals grains flatten and line up in parallel layers or bands.
Non foliated texture – mineral grains grow and rearrange but do not form layers.

18. Section 4 Sedimentary Rocks

19. Sedimentary rocks—mostly found on the exposed surface of the Earth
Rock fragments, mineral grains, and bits of plants and animal remains moved by wind, water, ice or gravity are called sediments
Sedimentary rocks form in layers
Sedimentary rocks—classified by what they were made of and how they were formed

20. Detrital sedimentary rocks—made from broken fragments of other rocks
When layers of small sediments stick together because of pressure, compaction occurs
When water and other minerals move through open spaces between larger sediments, gluing them together, cementation occurs.
Detrital rocks often have a granular texture

21. Rocks are named according to size and shape of sediments
Sediment size can be large like gravel or small like clay
Sediments can be well-rounded or have sharp edges
Chemical sedimentary rocks—non-clastic rocks formed when dissolved minerals came out of the solution
Limestone forms from calcite, which was calcium carbonate in solution
Rock salt forms from halite, which was salt in solution

22. Rock cycle—a continuous and dynamic process
Organic sedimentary rocks—made from remains of once-living plants or animals
Chalk—made of microscopic calcite-shell remains of animals
Coal—made of plant remains, chemically changed by microorganisms and compacted over millions of years
Rock cycle—a continuous and dynamic process