1. Geology Part II The Rock Cycle Rocks: Geologic Profiles Geologic Time
Igneous
Sedimentary
Metamorphic
Geologic Profiles
Geologic Time
Relative
Absolute
Radioactive Dating

2. Rocks are minerals?
an indefinite mixture of naturally occurring substances, mainly minerals.
various combinations of minerals and organic substances
range in size from tiny pebbles to mountains.
make up the earth’s crust.

3. Rocks are not always solid
As discussed in plate tectonics magma is liquid rock
While the composition of this basalt flow have the same composition,
the smooth pahoehoe lava was hotter than the jagged aa lava.
Soil and clay are other examples of nonsolid rock

4. Igneous Rocks Fire Formed Hardens as magma cools “original rock”
Lava is on the Earth

5. 2 types of Igneous Rocks 1. Intrusive cools inside the Earth
Slow cooling= big crystals
Ex.granite
2. Extrusive cools outside the Earth
Fast cooling = tiny crystals
Ex. obsidian

6. Types of Intrusive rocks
Granite is the most common and is referred to as “mountain guts”
Diorite – iron and magnesium
Gabbro – dark, large crystals
Peridotite – green, most of upper crust

7. Yosemite Rock formation http://www. nps
“El Capitan is the largest monolith of granite in the world.”
Formed deep underground and then uplifted by plate tectonics and shaped by erosion
Age can be determines by radioactive dating

8. Extrusive Igneous Rocks
Basalt – common, hard, dark
Andesite – began cooling in crust finished on surface large/small crystals
Rhyolite – cooled slowly then fast
Pumice – light, spongy look
Obsidian – volcanic glass, cools fast

9. Metamorphic Rock Created by 1 of 2 processes
Regional process – most common, heat and pressure over large area
Contact – heat and pressure next to magma chambers
2 types: Foliated, Nonfoliated
Formed from preexisting rock that has been exposed to high heat and/or pressure
Enough to deform but not melt
Cannot determine age by relative or absolute (radioactive dating)

10. Foliated “layered” rocks Slate – made from shale
Gneiss – made from granite

11. Nonfoliated No ‘layers’ Marble – made from limestone
Quartzite – made from quartz

12. Sedimentary Rock
Formed at the bottom of lakes and oceans by the deposition of sediment (small dust, sand, organic material) that was eroded by wind, water, ice from a preexisting rock.
Only 5% of Earth’s crust
Time and pressure cement particles to form a new rock

13. Sedimentary rock characteristics Breccia: clastic
Often have layers
Often contain fossils
Not very strong
Can determine relative age by location
Top layers are younger
Absolute age cannot be determined

14. 3 types: Clastic, Chemical, Organic
Clastic: Most common
Made of other rocks
Particles accumulate and harden in 2 ways
Weight of upper layers squeeze out liquids
Minerals dissolved in ground water act as cement
Weathering is an active process

15. Sandstone – sandsized quartz, variety of colors
Shale – most common, mud, clay, silts

16. Chemical Limestone – 50% calcite from seashells
Coquina – large pieces of shell
Chalk – microscopic pieces of shell

17. Halite – hard, created by evaporation
Gypsum – soft, created by evaporation
Chert – hard, created by heat

18. Organic
Coal – black, coarse, decayed plant life

19. Special Features of Sedimentary Rocks
Layering (bedding)
Fossils
Geode (minerals in a hole or cavity)
Concretions (minerals form around a grain or fossil)

20. Rock Cycle Interactive Review

21. Picture Credits
"Copyright 2009 by Andrew Alden, geology.about.com, reproduced under educational fair use.“
DeJuana Aldrich