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Unit 7 Rocks
Rocks
17
Science
6th Grade
12/07/2010

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Term
What are rocks?
Definition
Rocks are a mixture of minerals, rock fragments, volcanic glass, organic matter, or other natural material.
Term
What are igneous rocks?
Definition
Rocks formed from cooled or solidified magma.
Term
How are sedimentary rocks formed?
Definition
Sedimentary rocks are formed when eroded sediments are compacted and cemented
Term
How are metamorphic rocks formed?
Definition
Metamorphic Rock - formed when heat and pressure change an existing rock
Term
What is the rock cycle?
Definition
The rock cycle is a series of processes in which rocks continuously change from one type to another.
• Heat and pressure change rocks to metamorphic rocks deep underground
 Deeper rocks melt into magma then cool to form igneous rock
 Particles eroded from rocks form layers of sediment which are pressed together to form sedimentary rock
Term
What are extrusive rocks?
Definition
Extrusive rocks are formed from lava at the surface; also called volcanic rocks. These rocks
• Cool quickly
• Have small crystals
Examples:
Pumice: gasses are trapped to form bubbles; floats in water
Obsidian: has lost all of its gasses; also known as volcanic glass
Term
What are intrusive rocks?
Definition
Intrusive Rocks are formed from magma below the surface.
• Also called plutonic rocks.
• Intrusive rocks cool slowly and have larger crystals
• Batholiths are the largest of intrusive rocks; often form the bas of mountain ranges.
Term
What is porphyritic rock?
Definition
Porphyritic rock begins forming underground and is then forced out.
• Is considered to be partially intrusive and extrusive.
• Visually, one can see fine-grained crystalline material in which larger crystals are embedded
Term
What are some examples of igneous rocks?
Definition
• Granite – intrusive and light colored
• Gabbro – intrusive and dark colored
• Rhyolite – extrusive and light colored
• Basalt – extrusive and dark colored
Term
Describe the formation of sedimentary rocks
Definition
Pieces of broken rock are eroded and deposited in layers
2. Bottom layers are compacted and cemented by minerals
3. Lithification is the hardening of sediment into rock
Term
What is clastic rock?
Definition
Clastic rock is formed from mineral grains that have been compacted and cemented.
Examples:
• Conglomerate and breccia – large fragments
• Sandstone from sand, siltstone from mud, and shale from clay
Term
Describe organic rock.
Definition
Organic rock is formed from living things or their remains.
• Limestone, coal
Fossils are remains of dead animals or plants
Term
How is coal formed?
Definition
 Peat (roots, bark, spores, etc) are decayed by bacteria, compacted, heated over time.
 To become coal, this decaying peat must be buried by sedimentary rock.
 Over time, the peat is broken down, water is released, and is transformed into a carbon rich substance.
 Varies but 10-20 ft of peat = 1 foot of coal.
Term
Describe chemical rock.
Definition
Chemical rock is crystallized from evaporating solutions.
Example: Evaporites are from evaporating water.
Examples: the Great Salt Lake in Utah and the Dead Sea
Term
What is metamorphism?
Definition
Metamorphism is changes in structure, appearance, or composition of rock beneath the surface
• Contact Metamorphism – when magma contacts existing rock
• Regional Metamorphism – happens along plate boundaries
Term
What are foliated rocks?
Definition
Foliated rocks are rocks with grains arranged in parallel bands. Each band is made of a different mineral. Foliated rocks are formed from pressure in one direction.
Term
What are non foliated rocks?
Definition
Non foliated rocks are usually formed from rocks with only one mineral. Pressure is equal on all sides and the mineral grains are usually the same size.
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