Year 8 Geology

List the 4 layers of the Earth

The four layers of the Earth are the inner core, outer core, mantle, and crust.

Define ‘mineral’

A naturally occurring inorganic substance that make up rocks, for example salt

Define ‘rock’

A solid natural material made up of one or more minerals, for example sandstone

Define ‘soil’

the top layer of Earth’s surface, made up of minerals. Almost all Earth’s plants grow in soil

What are the three types of rocks?

Igneous, Sedimentary and Metamorphic

What is a mineral in terms of classifying minerals?

a regular repeating pattern that can form crystals

What is a crystal?

a mineral’s repeating pattern over and over again, which forms in geometric shapes

What is a gem

cut and polished crystals

What is a rock in terms of classifying minerals

Grains of different types of minerals

Colour

different minerals have different colours

Lustre

how shiny a material is or how well or reflects light

Hardness

Moh’s scale of hardness - the ability of a material to scratch other materials

Cleavage

the way minerals split or break

Streak test

the colour that is left behind when scratched on an unglazed white tile

Weathering

rocks breaking down into smaller peices, and can be classified into physical, chemical and biological weathering.

Physical weathering

when rocks break down into smaller peices by physical forces, for example temperature, water, wind, and freeze thaw

Biological weathering

The disintergration of rocks that is caused by living organisms, for example a burrowing animal

Chemical weathering

when rocks break down due to chemical reactions, for example acid rain in a highly polluted area

Erosion

carries rock fragments from one place to another. Agents of erosion include wind, water or gravity

Deposition

when sediment is deposited somewhere on the Earth’s surface, for example sediment falling off a cliff onto the land below

Rock cycle

The process where one type of rock can change into another type through physical processes

List 4 characteristics of sedimentary rocks

• foliations

• Often have fossils

• Grainy/soft texture

• May contain different rock particles

List 3 characteristics of metamorphic rocks

• foliations

• Hard and dense

• Can have shiny appearence

List 4 characteristics of igneous rocks

• may contain crystals

• May have holes from gas bubbles

• No layers

• Can be smooth or rough

How are clastic sedimentary rocks formed?

when small particles of rocks stick together. The process is deposition, bedding, compaction and cementation

How are organic sedimentary rocks formed?

made from dead organic materials (e.g. dead plants and animals) that are compacted and cemented. For example coal

how do you tell what layers of rocks are younger/older

oldest = at the bottom

Youngest = at the top

Lava

molten rock on the continental crust

Magma

molten rock under the continental crust

Features of intrusive igneous rocks

• large crystals that can be seen without magnifying glass

• Coarse texture

Features if extrusive igneous rocks

• Small crystals that require magnifying glass to see

• Glassy/fine

Metamorphosis

the heat and pressure inside the earth cause minerals in the rock to change and form new minerals e.g round pebbles become flattened

Contact metamorphosism

when a rock is altered by high heat in direct contact with magma. It often occurs near sources of magma e.g. volcanoes

Reginal metamorphosism

when a rock is altered by high pressure at plate boundries. There are no fossils because of the amount of pressure

Foliations

layers of bands that are mainly in reginal metamorphic rocks because of pressure

Features of diamonds in reginal metamophic rocks

• form when crust pushes into mantle

• Temperature and pressure

• Carried to the crust millions of years later by geological uplift

Geological uplift

The process of an increase in Earth’s surface elevation, which pushes rocks that were deep underground to the surface e.g. formation of mountains