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Classifying Rocks
What is a rock?
•Rocks are naturally occurring solid mixtures of one or more minerals or organic matter.
Rocks• A. Classifying Rocks• 1. Composition – Minerals they are made from• A. Some rocks contain only one mineral• B. Most rocks contain more than one mineral• i. 20 minerals form most of the rocks that
make up the earth’s crust
Texture• 2. Texture- look and feel of a rocks surface• Grain – particles made of minerals or other rocks
• A. Grain Size• 1. Fine Grain – small grain• 2. Coarse Grain – large grains• 3. no visible grains
• B. Grain Shape• 1. Rounded Grain• 2. Jagged Grain
• C. Grain Pattern• 1. Banded grain• 2. Non-banded grain
Types• A. Igneous Rocks- cooling of magma or lava• B. Sedimentary Rocks – particles of other rock or
remains of plants and animals are pressed and cemented together
• C. Metamorphic Rocks- existing rocks are changed by heat, pressure or chemical reactions
Igneous Rocks
Igneous Rocks• A. types by Texture- size of grains or crystals• 1. Extrusive Rock- magma or lava that cools and
hardens at or near the earth’s surface• a. rock cools very quickly• b. crystals are small, if any at all• c. Examples: basalt, obsidian, pumice, rhyolite
Igneous Rocks• 2. Intrusive Rock- magma that cools and hardens
within the earth• a. rock cools very slow• b. crystals are very large• c. examples: granite, gabbro, diorite
Igneous Rocks• Types by composition- amount of silica• 1. high silica content – light colored• a. Examples: Granite, rhyolite
• 2. low silica content – dark colored• a. Examples: gabbro, basalt
Igneous rocks
• Uses of Igneous Rocks•1. Granite- statutes, headstones, bridges, buildings, floors, kitchen counters•2. Pumice, abrasives for cleaning and polishing•3. Obsidian- ancient tools
Igneous Video• http://www.videojug.com/film/geology-igneous-
rocks
Sedimentary Rocks
Sedimentary Rocks• A. Process to form a sedimentary rock• 1. weathering and erosion• weathering- wind and water breaking rocks into smaller
pieces• Erosion- wind and water carrying away particles
Sedimentary Rocks• 2. Deposition- sediments settling out of the wind
or water
Sedimentary Rocks• 3. Compaction- process of pressing the sediments
together
Sedimentary Rocks• 4. Cementation- dissolved minerals crystalize and
glue particles of sediment together
Types of Sedimentary Rocks• 1. Clastic Rocks-rocks made from pieces of other
rock• a. shale – made of clay• b. sandstone – made from sand• c. conglomerate – mixture of different sized rounded
particles• d. breccia- mixture of different sized jagged particles
Types of sedimentary rocks• 2. Organic Rocks – made from the remains of
plants and animals• a. coal – made from plants• b. limestone – made from coral, clams and oyster shells
Types of Sedimentary rocks• 3. Chemical rocks – rocks made when minerals in
a solution crystalize• a. limestone – made from calcite dissolved in lakes, seas
or underground water• b. rock salt – made from evaporated oceans and seas
USES of sedimentary rocks• Sandstone – buildings• Limestone – buildings• Flint - Arrowheads
Process of Deposition
•Process in which material is laid down
Weathering, Erosion and Deposition
•All geological processes that make and destroy rock
Strata
•Strata = Layers•Stratification- process in which sedimentary rocks are arranged in layers
Organic materials…
•Sedimentary rocks are the only rocks with fossils
Metamorphic Rocks
Metamorphic Rocks• Metamorphic Rocks- existing rocks are changed
by heat and pressure• Meta- change• Morphism - forms
Types of Metamorphic rocks• Foliated Rocks- when minerals flatten out and line
up in bands or parallel layers due to pressure• a. gneiss forms from granite• b. slate forms from shale
Types of Metamorphic Rocks• 2. Nonfoliated Rocks- rocks that do not show
bandsNot enough pressure on the rock to form bands
a. marble forms from limestoneb. quartzite forms from sandstone
USES of metamorphic rocks• 1. Marble: buildings, statues, countertop• 2. Slate: flooring, roofing, chalkboards, pool tables
Metamorphic video• http://www.youtube.com/watch?
v=UrimDbTUalg&feature=relmfu&safety_mode=true&persist_safety_mode=1