Chapter 4Rocks

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 texture

3. 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

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

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

• Most of Earth’s minerals 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

Texture

Grains- Give the rock texture

What is texture?

Texture is the look and feel of the rocks surface.

The three grain sizes that make texture are:

1.Fine

2.Coarse

3.No visible

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

see

• Fine grain = microscopic and too small to see

There are two grain shapes:

1. Jagged

2. Round

There are two grain patterns:

1. Banded

2. Non- banded

There are three main groups of rocks

Igneous – 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 an existing rock is changed by heat, pressure or chemical reactions, forms deep underground

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

1. Igneous rocks are classified according to origin, texture and mineral composition

– Origin– Texture– Mineral composition

Intrusive and Extrusive

3. Extrusive rock is formed from lava that erupted onto the earth’s surface.

4. 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 5-7

Texture: 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 ContinuedMineral Composition

1. Most of the earth’s rocks contain the mineral silica.

2. 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 and obsidian

• Sharp tools for cutting or scraping

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.Erosion

2.Deposition

3.Compaction

4.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*

2. 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*

3. Deposition - the process by which sediment settles out of the water or wind carrying it

Sedimentary Rocks*Compaction*

4. 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*

5. 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

6. The 3 types of sedimentary rocks are:– Clastic– Organic– Chemical

Sedimentary Rock: Clastic7. Clastic rock- a sedimentary rock that forms when rock fragments are squeezed together

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

Sedimentary Rocks: Organic

8. Organic rock- forms where the remains of plants and animals are deposited in thick layers

– Ex. coal, limestone

Sedimentary Rocks: Chemical

1. Chemical- when minerals that are dissolved in a solution crystallize

– Ex. rock salt

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

1. Heat and pressure beneath the surface of the earth can change any rock into a metamorphic rock.

2. 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

3. Foliated = grains arranged in parallel layers or bands

– Ex. slate, schist and gneiss

Metamorphic Rock

4. Non-foliated = mineral grains are arranged randomly

– Ex. marble, quartzite

Uses of Metamorphic Rocks

5. Two of the most used metamorphic rocks– Marble – building and sculptures

• Lincoln Memorial

– Slate – flooring, roofing, walkways, chalkboards

The Rock Cycle

1. 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