Chapter 4

Rocks: Mineral Mixtures

Section 1: Understanding Rock

The Earth’s crust is made up mostly of rock Rock – is simply a solid mixture of crystals of

one or more minerals Rocks come in all shapes and sizes

The Value of Rock

Rock has been an important natural resource for as long as humans have existed Early humans used rocks as hammers and to make

other tools Arrowheads and knifes were made out of rock

Rocks have also been used for centuries to make buildings, roads, and monuments

Concrete is one of the most common building materials today

Rock is also very important to scientists What can be found by scientists in rock that give us

clues and evidence about past life on Earth?

The Rock Cycle

The rocks in the Earth’s crust are constantly changing

The way that rock forms determines what type of rock it is

The three major types of rocks are; 1) Igneous – is rock that forms from the cooling of

magma. Magma forms in the Earth’s lower crust and

upper mantle 2) Sedimentary – is rock that forms when sediments

are compacted and cemented together The sediments that form this rock come from

weathering and erosion 3) Metamorphic – is rock that forms when the texture

and composition of a preexisting rock is changed by heat or pressure deep underground

(see page 83)

The Nitty-Gritty on Rock Classification You now know that rocks are classified into three

main categories But these three main groups can be broken down into

smaller groups based on how and where the rock is formed

Scientists use composition and texture to further classify rocks Composition – is the minerals that the rock are made

of Texture – is determined by the size, shape, and grain

positions of the rock The texture of a rock is a good clue to how and where

the rock formed

Chapter 4 – Quiz 1

1) ________ is simply a solid mixture of crystals of one or more minerals

2) ________ is rock that forms from the cooling of magma.

3) ________ is rock that forms when sediments are compacted and cemented together

4) ________ is the minerals that the rock are made of 5) ________ is determined by the size, shape, and

grain positions of the rock Bonus - _________ is when magma cools beneath

the Earth’s surface

Answers

1) Rock 2) Igneous 3) Sedimentary 4) Composition 5) Texture Bonus - Intrusive

Section 2: Igneous Rock

Origins of Igneous Rock

The word igneous comes from the Latin word for “fire”

When magma or lava cools down enough it forms igneous rock

There are three ways that magma can form; 1) Temperature

Deep within the Earth temperatures are high enough to melt rock

2) Pressure Hot rocks under extreme pressure will not melt until

the pressure is released 3) Composition

When the composition of the rock changes

Igneous Rock Formations

Intrusive – when magma cools beneath the Earth’s surface Intrusive rock formations are name for their

size and the way they push into the surrounding rock

Extrusive – igneous rock that forms on the Earth’s surface Most volcanic rock is extrusive

Section 3: Sedimentary Rock

Through the process of erosion, sediment is formed and transported from one place to another

As new layers of sediment are deposited they eventually become compressed which causes the sediments to become “glued” together

Sedimentary rock forms near or at the Earth’s surface

The most noticeable feature of sedimentary rock is its layers – strata

Composition of Sedimentary Rock

Classic Sedimentary Rock Sedimentary rock made of fragments of other

rocks and minerals Chemical Sedimentary Rock

Sedimentary rock formed from solutions of minerals and water

This happens as rain water slowly makes its way to the ocean

As it travels it dissolves some of the rock mineral it passes through

Types include rock salt and limestone

Sedimentary Rock Structures

Many sedimentary rock features can tell you about the way the rock formed Stratification – how sedimentary rock is

layered

Section 4: Metamorphic Rock

The word metamorphic comes from the meta, meaning “changed” and morphos, meaning “shape”

Rock can undergo “metaporphism” by heat, pressure, or a combination of both

Origins of Metamorphic Rock

Most metamorphic

http://www.isaacsondesign-hosting.com/bridgettej/rockcycle/sedimentary_rock.html