1. Rocks and the Rock Cycle

2. The Rock Cycle
The continuous and reversible processes that illustrates how one rock changes to another.
“One rock is the raw material for another”.

3. Rock Cycle Processes – Crystallization

4. Rock Cycle Processes - Weathering

5. Rock Cycle Processes - Lithification

6. Rock Cycle Processes - Metamorphism

7. Characteristics of magma
Magma is molten rock that originates in the mantle, at depths of km.
Igneous rocks form from molten rock when it cools and crystallizes into the rock-forming minerals.
Magma that reaches the surface is called lava.

8. Igneous Rocks
Volcanic (extrusive) igneous rocks form from lava on the surface.
Plutonic (intrusive) igneous rocks from magma beneath the surface and are exposed later

9. Volcanic Rock – Rapid rate of cooling
Volcanic rocks crystallize from lava on the surface.
Lava contacts air and water and cools rapidly, inhibiting large crystal formation.
The most common volcanic rock is basalt.

10. Plutonic Rock – Slow rate of cooling
Plutonic rocks crystallize from magma in the interior of the crust, which are later exposed.
Magma is insulated and cools slowly, allowing large crystals to form.
Most common plutonic rocks are from the granite family.

11. Igneous Rock Classification
Texture
(overall appearance of rock, but especially pertains to mineral crystal size)
linked to how rock formed since crystal size depends on rate of cooling
Mineral composition – chemical makeup of magma or lava

12. Texture Size and arrangement of crystals
Slow cooling rate promotes the growth of fewer but larger crystals
Fast rate forms many small crystals
Very fast rate forms glass
Overall appearance (vesicles, glassy etc.)

13. Phaneritic - Coarse-texture
Figure 3.9 Both of these rocks are about 5 inches across. Although granite (A) and rhyolite (B) contain the same minerals, granite is coarse grained because it cooled slowly, but rhyolite is very fine grained because it cooled rapidly.
Granite

14. Aphanitic - Fine texture
Figure 3.9 Both of these rocks are about 5 inches across. Although granite (A) and rhyolite (B) contain the same minerals, granite is coarse grained because it cooled slowly, but rhyolite is very fine grained because it cooled rapidly.
Rhyolite

15. Porphyritic – Bimodal crystal size
Large crystals, phenocrysts, form slowly from magma.
Magma erupts; crystals are suspended in an aphanitic matrix, the groundmass. 15

16. Glassy texture – indicates lack of crystalline structure due to rapid cooling
Figure 3.7 Obsidian is natural volcanic glass. It contains no crystals. This sample is about 6 inches wide.
Obsidian

17. Granitic (Felsic) Composition
Composed of primarily of light silicates
Contains high amounts of silica (SiO2)
Major constituents of continental crust.

18. Basaltic (Mafic) Composition
Composed of dark silicates and calcium-rich feldspar
More dense than granitic rocks
Comprise the ocean floor as well as many volcanic islands.

19. Sediment
solid rock or mineral fragments transported and deposited by water, wind, ice or gravity
dissolved minerals which evaporate or precipitate from water, or are secreted by organisms
accumulate over time as loose unconsolidated layer.

20. Sedimentary rocks form when sediment from weathered and eroded rock is compacted or cemented into solid rock
Figure 3.2 Sedimentary layers of sandstone form steep cliffs above the San Juan River in Utah.
Fig. 3-2, p.46

21. Sedimentary rocks Formed by the lithification of sediment
compaction by burial
cementation by minerals from ground water
Sedimentary rocks contain evidence of past environments
Provide information about climate
Often contain fossils

22. Clastic Sedimentary Rocks composed of solid sediment from weathered rocks
sandstone
conglomerate
organic shale

23. Chemical Sedimentary Rocks
Composed of minerals precipitated from surface or ground water (chemical sediment).
The upper picture shows rock salt on the Bonneville Salt Flats.
The lower photo shows veins of rock gypsum embedded in mudstone.
Both of these chemical sedimentary rocks are examples of evaporites.

24. Biogenic Sedimentary Rocks
composed of sediment of biological origin (e.g. shell fragments, plant material).
The upper photo is limestone, composed of an ancient coral reef in the Guadaloupe Mountains of Texas.
The lower photo is of bituminous coal.
COAL

25. Coal Formation

26. Metamorphic rocks form when heat, pressure or chemical reaction alters existing rocks
Gneiss, a metamorphic Rock from Baffin Island, Canada.
Fig. 3-CO, p.44

27. Metamorphism
The transition of one rock into another by temperatures and/or pressures unlike those in which it formed.
Metamorphic rocks are produced from
Igneous rocks
Sedimentary rocks
Other metamorphic rocks

28. Metamorphism Progresses incrementally (low to high-grade)
Rock remains solid throughout process
Agents of metamorphism
heat (between 150° and 800° C)
pressure (5 km below the surface the pressure is about 1500 x greater than atmospheric pressure
chemically-active pore fluids.

29. Heat – from the Geothermal Gradient or rising magma

30. Pressure from overlying rocks

31. Low grade to high grade Metamorphism (left-right)

32. Types of Metamorphism
Contact or thermal metamorphism – usually caused by contact of a rising magma body with host rock
Regional metamorphism (mountain building) – caused by tectonic plate interactions
Hydrothermal metamorphism – chemical alterations from hot, ion-rich water

33. Changes due to metamorphism
recrystallization of mineral grains and chemical precipitates
Formation of new, stable minerals
Foliation – parallel alignment of minerals due to pressure.

34. Foliation

35. Granite is a common parent rocks of Gneiss (“Nice”)
Igneous Granite
Metamorphic Gneiss

36. Sandstone is the parent rock for quartzite
Sandstone - sedimentary
Quartzite - metamorphic

37. Limestone is the parent rock for marble
Limestone - sedimentary
Marble - metamorphic