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