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Geology Part II
• The Rock Cycle• Rocks:
– Igneous– Sedimentary– Metamorphic
• Geologic Profiles• Geologic Time
– Relative– Absolute– Radioactive Dating
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.
http://en.wikipedia.org/wiki/Sedimentary_rock
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
Igneous Rocks
• Fire Formed
• Hardens as magma cools
• “original rock”
• Lava is on the Earth
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
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
Yosemite Rock formationhttp://www.nps.gov/yose/planyourvisit/formations.htm
• “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
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
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)
Foliated
• “layered” rocks
• Slate – made from shale
• Gneiss – made from granite
Nonfoliated
• No ‘layers’
• Marble – made from limestone
• Quartzite – made from quartz
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
Sedimentary rock characteristicsBreccia: 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
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
• Sandstone – sandsized quartz, variety of colors
• Shale – most common, mud, clay, silts
Chemical• Limestone – 50%
calcite from seashells• Coquina – large
pieces of shell• Chalk – microscopic
pieces of shell
• Halite – hard, created by evaporation
• Gypsum – soft, created by evaporation
• Chert – hard, created by heat
Organic
• Coal – black, coarse, decayed plant life
Special Features of Sedimentary Rocks
• Layering (bedding)• Fossils• Geode (minerals in a
hole or cavity)• Concretions (minerals
form around a grain or fossil)
Rock Cycle Interactive Review
• http://www.learner.org/interactives/rockcycle/diagram.html
Picture Credits
• "Copyright 2009 by Andrew Alden, geology.about.com, reproduced under educational fair use.“
• http://www.learner.org/interactives/rockcycle/diagram.html
• DeJuana Aldrich
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