1. What is the “rock cycle”?
Warm Up
What is the “rock cycle”?
Use examples of the various rock types in your description. Even if you don’t know the answer, give it your best guess.

2. Rocks

3. What is a Rock? Naturally occurring solid aggregate of minerals
Earth’s outer solid layer, the lithosphere, is made of rock
Often covered by soil or water

4. What is a Rock?
Three types – classified by the processes that made them
Type changes!
This change is diagramed by the “rock cycle”

5. Types of Rocks
Igneous– form from solidification of molten (liquid) rock material.
Sedimentary– form from compaction and cementation of sediments
Metamorphic– form from re-crystallization of existing rock material.

7. What would cause a rock to melt!?!
Igneous Rocks
Rocks formed by solidification from a melt
What would cause a rock to melt!?!
Lava- Magma that reaches the surface (extrusive)
Magma- molten rock beneath the Earth’s surface (intrusive)

8. Extrusive Igneous - rocks formed from cooled lava
Extrusive Igneous - rocks formed from cooled lava. Fine- grained, cooled quickly on the Earth’s surface.
Obsidian
Intrusive Igneous-rocks formed from cooled magma. Coarse-grained, cooled slowly beneath Earth’s surface.
Granite

9. How Igneous Rocks Melt Different rocks have different melting points
Magma often a slushy mix of molten rock, gasses, and minerals – partial melting
Mix depends on temperature, pressure, water content and mineral composition
Closer to Earth’s core – hotter it gets (1500 C)
Approx Temp (C)
Molten Minerals
600
Quartz, micas
800
Ca/Na
1000
Pyroxene
1200
All molten

10. Geothermal Gradient Hot Cool Silica-rich rocks melt
at cooler temperatures
Melts are viscous
Silica-poor rocks melt at higher temperatures
Melts are very fluid
Hot

11. Extrusive Igneous Rock - Lava (Hawaii)

12. Extrusive Igneous Rock - Lava (Hawaii)

13. Extrusive Igneous Devil’s Tower, Wyoming
Los Tercios Waterfall, Suchitoto, El Salvador
Devil’s Tower, Wyoming

14. Intrusive Igneous Rock (Granite) – This granite cooled 30 kilometers under the surface

15. Coarse texture Glassy Texture
Texture- the “feel” of a rock due to the grain size, shape, and arrangement of mineral crystals or sediments in a rock
Coarse texture
Glassy Texture

16. Grain Size- the diameter of individual grains of sediment
Grain Size- the diameter of individual grains of sediment. Geologists often make thin sections – very thin slices that light can pass through – to view grain size.
Thin sections under a microscope
Thin section to examine grain size

17. Grain Size
Fine grained – individual mineral grains are too small to be seen without a microscope.
Coarse grained – can see individual grains.

18. Small crystals (fast cooling)

19. Large crystals (slow cooling)

20. High silica, warm, viscous
Fine crystals
Need a microscope
Low silica, HOT, fluid
Intermediate
High silica, warm, viscous
Coarse crystals
Easily seen

21. Some Common Rock Descriptors
Felsic: silicate minerals, magma, and rocks which have the lighter elements such as silicon and oxygen. Usually light in color and specific gravities less than 3. Quartz and Granite
Mafic: silicate mineral or rock rich in magnesium and iron. Usually dark in color and relative density greater than 3. Basalt.

22. Origin of Granitic Rocks
Huge blobs w/ low temps but lots of magma, fractionation & assimilation => Granite Batholiths
Can also get subduction-generated granites folded in collisions, or from deep rock burial