Rocks and The Rock Cycle

What is a Rock?• A rock is a mixture of one or more minerals, glass, and

sometimes, consolidated organic material (something that was once living).

• We classify rocks into 3 categories based on how they were formed:• Igneous• Sedimentary• Metamorphic

Igneous Rocks• The term igneous comes from the Latin word ignis, which

means “fire” because early geologists often associated igneous rocks with fiery lava flows.

• They are formed from the crystallization of magma.• Bowen’s reaction series tells us when and how the crystal form.

Igneous Rock Continue • Igneous Rocks are the most common rock in the Earth’s crust.• There are two types of Igneous rocks:• Extrusive: fine-grained igneous rocks that cool quickly on Earth’s

surface• Intrusive: coarse-grained igneous rocks that cool slowly beneath

Earth’s surface

Intrusive Extrusive

Classifying Igneous Rocks• Once Igneous Rock have been classified has either intrusive or

extrusive they are then classified by their mineral compositions.

• Mineral Composition:• Felis: rocks such as granite are light-colored have high silica

contents, and contain quartz and the feldspar orthoclase and plagioclase.

• Mafic: rocks such as gabbro are dark-colored, have lower silica contents, and are rich in iron and magnesium.

Classifying Continued• Intermediate: is between felsic and mafic• Ultramafic: such as peridotite and dunite, have low silica

contents• Texture:• Extrusive rocks:

• Glassy or Fine-grained• Intrusive Rocks:

• Coarse-grained or Very Coarse-grained

• Look at the following table:

Classifying Igneous Rock TableExtrusive Felsic Intermediat

eMafic Ultramafic Texture

Obsidian Basaltic Glass

Glassy

Rhyolite Andesite Basalt Fined grained

Intrusive Granite Diorite Gabbro Peridotite Dunite Coarse-grained

Pegmatite Very Coarse-grained

Sedimentary Rocks• They are formed by sediments that have become cemented

together.• Sediments are pieces of solid material that have been deposited

on Earth’s surface by wind, water, ice, gravity, or chemical precipitation.

• Sedimentary rocks can be formed from metamorphic, igneous, or other sedimentary rocks that have been broken down by weathering and erosion.

Sedimentary Continue• Many components make it possible for Sedimentary rocks to

form:• Weathering is a set of physical and chemical processes that break

rock into smaller pieces• Erosion and Transport is the removal and movement of surface

materials from one location to another. The four main agents of erosion are: wind, moving water, gravity, and glaciers.

• Deposition is when sediments are laid down on the ground or sink to the bottom of bodies of water

• Lithification is the physical and chemical processes that transform sediments into sedimentary rocks

• Cementation occurs when mineral growth cements grains together into solid rock.

Classifying Sedimentary Rocks• The classification of sedimentary rocks is based on how they

were formed.• There are three main groups:• Clastic: formed from the abundant deposits of loose sediments• Organic: formed from the remains of once-living things• Chemical: water evaporates and the minerals are left behind

Classifying Sedimentary Rock Table

Rock Type Rock Name Method of Formation

Clastic•Coarse grained•Medium grained•Fine grained

Conglomerate or BrecciaSandstoneShale

Lithification of clastic sediments

Organic•Calcium carbonate-shells•Plant matter

Limestone Coal

Accumulation and lithification of remains of living things

Chemical•Calcite•Halite•Gypsum

LimestoneRock SaltRock Gypsum

Precipitation of dissolved minerals from water

Metamorphic Rocks• They are formed deep inside the Earth. Heat and pressure

from the rock above flatten and bend the rock or even exchange atoms, forming new minerals.

• Metamorphic rocks have two categories:• Foliated: wavy layers or bands of minerals form in the rock• Non-Foliated: are composed of minerals that have blocky crystal

shapes.• Metamorphic rocks are created from sedimentary, igneous,

and other metamorphic rocks

Metamorphic Rocks

Foliated Non-Foliated

The Rock Cycle• The Rock Cycle helps us learn how each of the different rocks

are formed.• It is called a cycle because the rocks can travel in more than

one path.• The rocks of the Earth’s crust are constantly being recycled

from one type to another.• See below, the arrows represent the different processes that

change rocks into there different types.

Rock Cycle diagram