Geology Part II The Rock Cycle Rocks: Geologic Profiles Geologic Time 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 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

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 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

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