Rocks

What are Rocks?

How are these rocks different from one another?

How are they similar?

• A rock is a naturally occurring solid mixture of one or more minerals, or organic matter.

• Rocks are classified by how they are formed, their composition, and texture.

What are Rocks?

Types of rocks according to ORIGIN:

1.IGNEOUS2.SEDIMENTARY3.METAMORPHIC

What are Rocks?

• Igneous rock begins as magma.

• Magma is a mixture of many minerals

Igneous Rocks

magma

volcano

1. Texture• Coarse-grained texture is caused by

slow cooling resulting in larger crystals.

• Fine-grained texture is caused by rapid cooling resulting in smaller, interconnected mineral grains.

Igneous Rocks

Classification of Igneous Rocks

Texture (continued)• Glassy texture is caused by very rapid cooling.

• Porphyritic texture is caused by different rates of cooling resulting in varied sized minerals.

2. Composition• Granitic composition rocks are made mostly of light-

colored quartz and feldspar.

Igneous Rocks

Classification of Igneous Rocks

• Basaltic composition rocks are made mostly of dark-colored silicate minerals and plagioclase feldspar.

• Andesitic composition rocks are between granitic light-color minerals and basaltic composition dark-colored minerals.

• Ultramafic composition rocks are made mostly from iron and magnesium-rich minerals.

2. Composition (continued)

Classification of Igneous Rocks

Igneous Rocks

Igneous Rocks

Felsic

Mafic

Coarse-Grained

Fine-Grained

Granite

Gabbro Basalt

Rhyolite

Igneous Rocks

• Intrusive Igneous Rocks: when magma pushes into surrounding rock below the Earth’s surface

• Extrusive Igneous Rocks: when magma erupts onto the Earth’s surface (lava), cools quickly with very small or no crystals formed

http://www.windows.ucar.edu/tour/link=/earth/geology/ig_intrusive.html&edu=high&fr=t

Igneous Rocks

Obsidian

What is Obsidian?

Obsidian is a dark-colored volcanic glass that forms from the very rapid cooling of molten rock material. It cools so rapidly that crystals do not form.

Obsidian is a dark-colored volcanic glass that forms from the very rapid cooling of molten rock material. It cools so rapidly that crystals do not form.

Is this rock Felsic or Mafic?

Is it fine-grained or coarse-grained?

Is this rock Intrusive or Extrusive?

Mafic, fine grained, extrusive

Igneous Rocks

http://www.fi.edu/fellows/payton/rocks/create/sediment.htm

• Sedimentary rock is formed by erosion.• Sediments are deposited in layers, with the older ones

on the bottom.

Sedimentary Rocks

sea

Fragments washed to the sea

Sedimentary rocks

Rocks are brokenup by the actionof weather

Getti

ng older

The layers become compacted and cemented together.

Sedimentary Rocks

Stratification is the process in which sedimentary rocks are arranged in layers

Sedimentary Rocks

1. Clastic/detrital sedimentary rocks are made of fragments of rock cemented together with calcite or quartz.

Breccia is a term most often used for clastic sedimentary rocks that are composed of large angular fragments (over two millimeters in diameter).

Sedimentary Rocks

Classification of Sedimentary Rocks

2. Minerals crystallize out of solution to become chemical sedimentary rocks.

Limestone is a sedimentary rock composed primarily of calcium carbonate (CaCO3) in the form of the mineral calcite. It most commonly forms in clear, warm, shallow marine waters.

Sedimentary Rocks

3. Organic sedimentary rocks are formed from the remains of plants and animals.

Coal is an organic sedimentary rock that forms from the accumulation and preservation of plant materials, usually in a swamp environment.

Sedimentary Rocks

Sedimentary Rocks

Classification of Sedimentary Rocks

http://www.fi.edu/fellows/payton/rocks/create/metamorph.htm

•Meaning to change shape•Changes with temperature and pressure, but remains solid•Usually takes place deep in the Earth

Metamorphic Rocks

Magma

Pressure from surface rocks

metamorphicrock forms here

heat

1. Contact Metamorphism ~ heating by nearby magma

Hornfels is a fine-grained non-foliated metamorphic rock produced by contact metamorphism

http://www.windows.ucar.edu/tour/link=/earth/geology/meta_contact.html&edu=h igh&fr=t

Metamorphic Rocks

Metamorphic rocks form by:

2. Regional Metamorphism ~ pressure builds up in rocks that is deep within the EarthLarge pieces of the Earth’s crust collide and the rock is deformed and chemically changed by heat and pressure.

http://www.windows.ucar.edu/tour/link=/earth/geology/meta_regional.html&edu=high&fr=t

Metamorphic Rocks

Classification of Metamorphic Rocks

1. Foliated Metamorphic Rock

2. Nonfoliated Metamorphic Rock

Two main categories

• Has a banded or layered appearance

• Does not have a banded texture

Metamorphic Rocks

Metamorphic Rocks

Foliated ~contain aligned grains of flat minerals

Gneiss is foliated metamorphic rock that has a banded appearance and is made up of granular mineral grains.

Metamorphic Rocks

Non-Foliated ~mineral grains are not arranged in plains or bands

Marble is a non-foliated metamorphic rock that is produced from the metamorphism of limestone.

Metamorphic Rocks

http://www.avangstone.com/images/stone_info/images/marble.jpg

Determine if the following rock samples are foliated or non-foliated:

Amphibolite Quartzite Phyllite

Metamorphic Rocks

NF NF F

The Rock Cycle

Does marble remain as marble forever?

Can limestone (sedimentary) become marble (metamorphic)?

The Rock Cycle

http://www.gsi.ie/NR/rdonlyres/1796E90B-730D-4230-9AC3-CDB27F5F09E8/0/Rock_Cycle.bmp