Igneous ROCK

igneous rock – formed from magma or lava

classified by

1. origin

where formed?

on or beneathEarth’s surface

2. texture

depends on size & shape

of mineral crystals

3. mineralcomposition

Silica content

1. Origin• extrusive rock= formed from lava on

Earth’s surface–ex. basalt

• intrusive rock= formed from magma below Earth’s surface–ex. granite

2. Texture• depends on size & shape of mineral crystals

different textures1. fine-grained • small crystals or no crystals

• rapid cooling

2. coarse-grained • large crystals • slow cooling

3. porphyritic • large crystals surrounded by smaller crystals• magma cools slowly- then rapidly

4. glassy • no crystals form • extremely rapid cooling

coarse-grained fine-grained

porphyritic

3. Mineral Composition• lava low in silica dark colored rocks

– Examples: basalt, scoria

• lava high in silica light colored rocks– Examples: granite, pumice

Uses of igneous rocks

• hard, dense, & durable• ex:

1. granite• Used for building material

statuesCountertops, floors

2. pumice• good abrasive for cleaning & polishing

3. basalt• Used in making gravel in construction

• Cooling lava forms extrusive rock with small or no crystals

• Cooling magma forms intrusive rock with large crystals

Sedimentary ROCK

Sedimentary rocks are the second great rock class. Whereas igneous rocks are born hot, sedimentary rocks are born cool at the Earth's surface, mostly under water. They usually consist of layers or strata, hence they are also called stratified rocks.

IDENTIFYING SEDIMENTARY ROCKS

Small rocks, fragments and organic remains that have been moved by water, wind or other agents of erosion are called sediment.

1. Mechanical weathering: a rock is broken down without changing its mineral make-up.

Ex: waves, wind, running water, gravity

Sedimentary rocks are the result of the following processes:

2. Chemical weathering: a rock is broken down by chemical reactions that change its mineral composition.

Ex: oxidation (rusting) & acid rain

3. Erosion: the process where weathered material (sediments)

get carried away

4. Deposition: the process by which sediments settle down

in a NEW location

Over time, sediment is compacted and cemented together.

1. Compaction• Sediments are deposited, layer upon layer

builds up.

Sedimentary RocksSedimentary Rocks

• Pressure from the upper layers pushes down on the lower layers.

• If the sediments are small, they can stick together and form solid rock

2. Cementation• If sediments are large, like sand and pebbles, pressure

alone can’t make them stick together. • Large sediments have to be cemented together. • As water moves through soil and rock, it picks up

dissolved minerals such as quartz and calcite. These minerals are deposited between the sediments.

• Upon solidifying, these minerals, acting as natural cements, hold the sediment together like glue, making

clastic sedimentary rock.

Sedimentary RocksSedimentary Rocks

Stacked Rocks

Sedimentary rocks often form as layers. The older layers are usually on the bottom because they were deposited first.

Sedimentary RocksSedimentary Rocks

Layered rock is also calledSometimes, forces within Earth overturn

layers of rock, and the oldest are NO longer on the bottom.

Sedimentary rocks account for 75% of the rocks exposed at the Earth’s surface

intrusion

Label theOldest layer?

Youngest layer?

There are Three Major

Types of Sedimentary

Rocks

1. Clastic rock- sedimentary rock formed from rock fragments of other rocks (mentioned above)

• Clastic rocks have granular textures, much like sugar.

• They are named according to the shapes and size of the sediments that form them.

Sedimentary RocksSedimentary Rocks

From smallest to largest

ExamplesConglomerates: Conglomerate rocks are made of large rock pieces that have been cemented together. When looking at this rock type, you can easily see the parts that it has been made of. Pushing hard on single rock pieces in the conglomerate may result in these pieces being broken off of the rock.

Sandstone: Sandstone rocks are made of fine sand grains. Like conglomerate, the grains of sand have been cemented together. Rubbing the surface of sandstone rocks may result in small grains of sand being rubbed off of the rock.

Shale: Shale is made up of very fine grains of clay like particles. The texture of shale is very smooth to the touch. If you apply pressure to the shale, it is possible to break it into pieces that also have smooth textures.

2. Organic rocks sedimentary rocks formed from the life processes or remains of living organisms

Fossil-rich Limestone, made from the mineral calcite, is formed from the shells of clams, mussels, corals and snails.

Coal is made from plants that died in swamps millions of years ago.

Organic Sedimentary Rocks

If a rock is made completely of shell fragments that you can see, the rock is called coquina (koh KEE nuh).

3. Chemical Rocks• Chemical sedimentary rocks formed when

dissolved minerals come out of solution.

• Minerals collect when seas or lakes evaporate. The deposits of minerals that come out of solution form sediments and rocks.

• Chemical sedimentary rocks are NOT made from pieces of preexisting rocks.

Halite is an example of a rock that formed when water evaporated and left behind minerals. Halite forms rock salt. Companies mine these deposits because rock salt is an important resource.

Chemical limestone forms when calcite comes out of a solution in ocean water. Limestone can contain other minerals but must be at least 50% calcite

Metamorphic ROCK

• Rocks that have changed because of changes in temperature and pressure or the presence of hot watery fluids are called metamorphic rocks.

• Metamorphic rocks can form from igneous, sedimentary, or other metamorphic rocks.

• Each type of metamorphic rock can come from several kinds of parent rocks.

• Depending upon the amount of heat & pressure applied, one type of rock can change into several different metamorphic rocks.

1. Rocks beneath Earth’s surface are under great pressure from rock layers above them.

• Temperature also increases with depth in the Earth.

Example of Metamorphic Transition

The sedimentary rock shale will change into slate.

As increasing pressure and temperature are applied, the slate can change into phyllite, then schist, and eventually gneiss.

SlateShale

Slate Phyllite Schist Gneiss

Schist also can form when basalt is metamorphosed, or changed, and gneiss can come from granite.

Basalt

SchistGneiss

Granite

2. Hot Fluids, which are mostly water with dissolved elements and compounds, can react chemically with a rock and change its composition.

• This is what happens when rock surround a hot magma plume reacts w/ these fluids

• Most fluids that transform rocks during metamorphic processes are hot and mainly are comprised of water and carbon dioxide.

• In the presence of hot, water-rich fluids, solid rock can change in mineral composition without having to melt.

Metamorphic rocks can be classified according to composition and texture

• Foliated (texture)- when mineral grains line up in parallel layers (dark/light bands)

Examples: gneiss (NISE) (parent rock granite) & slate (parent rock shale)

• Non-Foliated (texture)- when mineral grains grow and rearrange but do NOT form layers

Examples: marble (parent rock limestone) & quartzite (parent rock sandstone)

Development of foliation dueto directed pressure (stress)

Foliated Nonfoliated

The Rock Cycle• The rock cycle is a continuous cycle

and a dynamic process!• The processes of melting, cooling,

heat & pressure, weathering, erosion, deposition, compaction & cementation slowly change rock from one kind to another…the cycle NEVER ends!

The Rock Cycle