Chapter 4Rocks

Classifying Rocks

Section 1

Why must scientists who study rocks look at the inside of them? Because the outside surfaces have been

exposed to the effects of ice, water, and weather (Erosion).

Mineral composition and color

2. What three important things do scientists observe when studying rocks?

-Mineral composition, color, and texture3. What are rock forming minerals?

-About 20 minerals that are found in the earth’s crust that make up rocks.4. What minerals are found in granite?

-Quartz, horneblende, mica, and feldspar

Mineral Composition:(This is also in the igneous section on page 2)

Most of Earth’s (rocks) contain Silica Silica is a material formed from oxygen and

silicon. The silica content of magma and lava will

affect the types of rock that form High silica usually forms light colored rocks Low silica usually forms dark colored rocks

5.Some other ways scientists study rocks include:

Shape and color of the crystals Mineral content Color Texture And some other tests similar to the tests for

minerals

TextureGrains- Give the rock textureWhat is texture?Texture is the look and feel of the rocks surface.The three grain sizes that make texture are:1.Fine2.Coarse3.No visible

Texture: Grain Size Coarse grained = large grains and easy to see

Fine grain = microscopic and too small to see

There are three main groups of rocksIgneous – forms from cooling of magma or lava

Sedimentary – forms when particles of other rocks or the remains of plants and animals are pressed and cemented together

Metamorphic – forms when and existing rock is changed by heat, pressure or chemical reactions, forms deep underground

There are two grain shapes:1. Jagged 2. Round

There are two grain patterns:1. Banded 2. Non- banded

Igneous Rocks

Section 2

Igneous Rocks An igneous rock is any rock that forms from

magma or lava. The name “igneous” comes from the Latin

word meaning “fire” Igneous rocks come from deep within the

ground

Igneous Rock Identification Igneous rocks are classified according to

origin, texture and mineral composition Origin Texture Mineral composition

Intrusive and ExtrusiveExtrusive rock is formed from lava that erupted onto the earth’s surface.

Intrusive rock is formed when magma hardens beneath the surface.

Molten rock below the earth’s surface is called magma. When it makes it to the surface it is called lava.

Igneous IDQuestions 5-7Texture: depends on the size and shape of the mineral crystals. The only exceptions are those rocks made of glass.

Rapidly cooling lava forms fine-grained rock Slowly cooling lava forms coarse-grained rocks

with large crystals Intrusive rocks should have coarse-grained

texture while extrusive rock will have fine-grained texture.

Igneous Rocks Continued Most of the earth’s rocks contain the mineral

silica. Silica content of rocks can affect the rocks

color.Examples of Igneous rocks:Rhyolite, Porphyry, Pegmatite, Granite, etc.

Uses of Igneous Rock Building Material

granite Cleaning and polishing

Pumice Sharp tools for cutting or scraping

obsidian

Sedimentary Rocks

Section 3

Sedimentary RockSediment - small, solid pieces of material that come from rock or living things.

Ex. rock, shells, bones, leaves, stems, etc.Sedimentary rocks are formed through the process of:

1.Erosion2.Deposition3.Compaction4.Cementation

Rocks

From Sediment to Rock

Most sedimentary rocks are formed through a series of processes: erosion, deposition, compaction, and cementation.

- Sedimentary Rocks

Sedimentary Rocks*Erosion*Erosion- destructive forces including heat, cold, rain, waves, grinding ice, running water, wind and ice loosen and carry it away. (The forces of erosion form sediment)

Sedimentary Rocks*Deposition*Deposition - the process by which sediment settles out of the water or wind carrying it

Sedimentary Rocks*Compaction*

Compaction - the process that presses sediments together

Thick layers build up over millions of years The more layers, the more it presses down on the

layers beneath them.

Sedimentary Rocks*Cementation*

Cementation - the process in which dissolved minerals crystallize and glue particles of sediment together

While compaction is occurring, the minerals slowly dissolve in the water

Sedimentary Rocks 3 major types of rocks

Clastic Organic Chemical

Sedimentary Rock: ClasticClastic rock- a sedimentary rock that forms when rock fragments are squeezed together

Sediments can range in size Ex. shale, sandstone, conglomerate, breccia

Sedimentary Rocks: OrganicOrganic rock- forms where the remains of plants and animals are deposited in thick layers

Ex. coal, limestone

Sedimentary Rocks: ChemicalChemical- when minerals that are dissolved in a solution crystallize

Ex. rock salt

Rocks From Reefs

Section 4

http://www.youtube.com/watch?v=60jof35WuAo

http://www.brainpop.com/science/diversityoflife/coral/

Rocks from Reefs1.These rocks are made from the exoskeletons of coral animals.2. Life can only live within the first 40 meters because that is where there is enough light.3. The exoskeletons are made from calcium.4. A coral reef forms when the animals die and their skeletons remain building up over time.5. Temperatures must be warm.6.Limestone deposits can tell us that there must have been on ocean or sea there sometime in the past

Metamorphic Rocks

Section 5

http://www.brainpop.com/science/earthsystem/typesofrocks/

Metamorphic RocksHeat and pressure beneath the surface of the earth can change any rock into a metamorphic rock.Geologists classify metamorphic rocks according to the arrangement of the grains that make up the rocks

Foliated Rocks Non-foliated Rocks

Metamorphic Rocks When a rock becomes a metamorphic rock…

Its appearance changes Texture changes Crystal structure changes Mineral content changes

Metamorphic Rocks Foliated = grains arranged in parallel layers or

bands Ex. slate, schist and gneiss

Metamorphic Rock Non-foliated = mineral grains are arranged

randomly Ex. marble, quartzite

Uses of Metamorphic Rocks Two of the most used metamorphic rocks

Marble – building and sculptures Lincoln Memorial

Slate – flooring, roofing, walkways, chalkboards

The Rock Cycle

Section 6

The Rock Cycle

Forces deep within the Earth and at the surface, produce a slow cycle that builds, destroys, and changes the rocks in the crust.

The rock cycle is a series of processes that change rocks from one kind to another.

Quartz

Sediment

Compaction

Cementation

Sedimentary Rock (sandstone)

Buried Pressure

Heat

Metamorphic Rock (quartzite)

What next?

ROCK CYCLE ACTIVITY