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