Chapter 4: Rocks

What is a rock?

• A ROCK is a mixture of minerals, mineraloids, glass, or organic matter.

3 Main Categories of Rocks

1.Igneous Rocks

2.Metamorphic Rocks

3.Sedimentary Rocks

Rock Cycle

• The process by which, over many years, Earth

materials form and change back and forth

among igneous rocks, sedimentary rocks, and

metamorphic rocks.

* The rock cycle can start with any rock – it is a

cycle

Processes of the Rock Cycle

Weathering-breaking of rocks into smaller pieces, either mechanically or chemically

Erosion-the process that wears away surface materials and moves them from one location to another, usually by gravity, glaciers, wind, or water.

Compaction-pressing sediments of rock together

Cementation-sediments naturally being glued together

Sediments-made from loose rock fragments

Igneous Rock Vocabulary• Igneous Rock-most abundant rock on Earth

because its inside and outside the earth, formed from magma and lava

• Intrusive-forms inside the earth from magma

• Extrusive-forms outside the earth from lava

• Granitic-magma is light colored, light weight, low density rocks like Pumice and Granite (Silicon,Oxygen)

• Andesitic-magma is of medium color and density, characteristics of both Basaltic and Granitic

• Basaltic-magma is dark colored, heavy rich in Iron and Magnesium, higher density.

*Density is how highly packed a substance’s molecules are. Mass/Volume.

Igneous Rock Examples

GranitePumice

Obsidian

Scoria

Facts about some Igneous Rocks

• Basalt – has iron in it and contains some air pockets.

• Pumice – is porous, and less dense than water so it will float.

• Obsidian – is glass like.

Minerals that make up Granite…

• Feldspar

• Quartz

• Mica

• Hornblend

• and others.

Metamorphic Rocks• Metamorphic-rocks that have changed due to

heat and pressure

• Foliated- type of metamorphic rock created when mineral grains flatten and line up in parallel bands

• Nonfoliated-type of metamorphic rock created when mineral grains change, grow, and rearrange – but do not form bands.

Metamorphic Rock Examples

Slate - foliated Marble – nonfoliated

Gneiss - foliated Quartzite – nonfoliated

Sedimentary Rocks

• Sedimentary Rocks-form when sediments get pressed or cemented together (Cementation and Compaction)

• Organic-made from the remains of once living things.

• Detrital/Clastic-made from broken rock fragments. They have texture.

• Chemical-when minerals precipitate out of a solution or left behind when a solution evaporates.

What is a Conglomerate?

• Conglomerate – sedimentary rock made of large well-rounded stones that have been cemented together.

Sedimentary Rock Examples

Shale - detrital Limestone - chemical

Coquina - organic Sandstone - detrital

Coal - organic

Conglomerate - detrital