Chapter 6: RocksChapter 6: Rocks

Chapter 6.1Chapter 6.1

How Rocks FormHow Rocks Form

What Is A Rock?What Is A Rock?

• Rock is a group of minerals bound together.

• Rocks are classified by the processes that they form under.– Igneous – formed from the cooling of hot molten

rock– Sedimentary – formed by the compaction and

cementation of sediments– Metamorphic – formed the heat and pressure on

pre-existing rock

The Rock CycleThe Rock Cycle

• Classifies the rocks of the crust according to their origin

Chapter 6.2Chapter 6.2

Igneous RockIgneous Rock

Igneous Rock FormationIgneous Rock Formation

• Felsic Magma – Very thick and slow moving– Contains large amounts of silica– Light-colored minerals quartz and orthoclase

feldspar

• Mafic Magma– Hotter and more fluid– Contains large amounts of iron and

magnesium– Formed dark silicate minerals hornblende

augite and biotite

Where FormedWhere Formed

• Underground magma– Cools slower which allows larger gains known as a

coarse texture

• At the surface– Cools fast minerals are microscopic of nonexistent– Small crystals considered fine grain texture– No crystals considered glassy texture– Porphyry – texture where large crystals are

surrounded by a fine-grained mass rock

Igneous Rock DescriptionsIgneous Rock Descriptions

– Igneous rocks are grouped into families according to their mineral composition

• Granite Family– Form from felsic magma– Granite itself is the intrusive coarse-grained member

of this family that is found in many mountainous areas in the U.S.

– Obsidian – chemical composition resembles granite but has a glassy texture and dark color

– Pumice – contains a many air holes and has a glassy texture

– Rhyolite – fine grain igneous rock that is light in color

• Gabbro Family– Form from mafic magma– Gabbro itself is a coarse-grained dark igneous

rock– Basalt – the most common it is fine grained– Scoria – glassy texture with air holes

• Diorite Family– Neither felsic nor mafic– Intermediate in color grays to green– Diorite – coarse grain– Andosite – fine grain

• Igneous Intrusions– Pluton – a rock mass that forms when magma

cools inside Earth’s interior– Dykes – Pluton of Igneous sheet rock that

cuts across rock layers– Sill – Pluton of Igneous sheet rock that lies

parallel to the rock layers– Batholiths – the largest plutons form the core

the mountain ranges

Chapter 6.3Chapter 6.3

Sedimentary RockSedimentary Rock

– Formed from the compacting and cementing of sediments

Clastic Sedimentary RockClastic Sedimentary Rock

• Formed from fragments of other rock

• Formations of clastics begins with the movement and relocation of fragments

• Usually transported by running water which deposits them into a body of water– River – bay

• The lighter the material the farther from shore they are carried– Particles are sorted by size– The largest gravels fall out 1st forming

conglomerates followed by sands then clays

• The particles of the rocks become cemented together– Silica cements are more durable than calcite

cements

Chemical Sedimentary RockChemical Sedimentary Rock

• These rocks form when minerals precipitate or falling out of a solution– Rock salt (halite), gypsum and some

limestone

Organic Sedimentary RockOrganic Sedimentary Rock

• Consists of sediments from the remains of plants and animals– Coal and limestone (shells)

Features of Sedimentary RockFeatures of Sedimentary Rock

• Stratification – arrangement of visible layers• Bedding Plane – line between different layers of

rock• Fossils – round only in Sedimentary rock it is the

remains, impression or any evidence (tracks) of a plant or animals

• Ripple marks• Nodules – fine grain silica found in limestone• Geodes – spheres of silica rock found in

sandstone

Chapter 6.4Chapter 6.4

Metamorphic RockMetamorphic Rock

– Formed from pre-existing rock (parent rock)

Metamorphism – rocks structure is Metamorphism – rocks structure is changed by pressure, heat and moisturechanged by pressure, heat and moisture

• Regional Metamorphism – occurs in mountain building areas

– The more pressure and the higher the temperatures – higher the morph

• Local Metamorphism –

– Contact – where magma touches existing rock

• Shale becomes horn fells which is dense and fine grained rock

– Deformation – occurs along fault lines where the heated created by friction cause the rock to change

Metamorphic Rock Metamorphic Rock DescriptionsDescriptions

• Foliation – tendency of rocks to form layers with visible minerals

• Non foliated –– Banded – light and dark colors– Non-organized –

• Sandstone quartzite • Limestone marble