Rock Classification
By: Kristin Strickland
What is a rock?
A rock is a solid mineral material forming part of the surface of the earth and other similar planets. There are three different types of rock on Earth. There are igneous, sedimentary and metamorphic rocks.
Igneous Rock
- Igneous rocks are formed by cooling and crystallization of molten rock.
- Igneous rocks can be formed inside of a volcano or outside of a volcano.
- There are two main types of igneous rocks, intrusive and extrusive.
- Intrusive rocks are formed inside of a volcano slowly which form larger crystals.
- Extrusive rocks are formed outside of the volcano quickly which form much smaller crystals.
Sedimentary Rock
- Most sedimentary rocks are composed primarily of the weathered remains of other rocks which form on the surface of the Earth.
- Sedimentary rocks are usually formed by the compaction and cementing of sediments.
- There are three types of sedimentary rocks. Clastic, bioclastic and crystalline.
- Clastic rocks are made up of different sized particles cemented together.
- Bioclastic rocks are formed by the accumulation of plant and animal remains containing shells or plant materials.
- Crystalline rocks are deposited when chemicals in seawater precipitate and fall to the ocean water.
Metamorphic Rock
- Metamorphic rocks form when other rocks are exposed to heat and/or pressure without melting.
- Metamorphic rocks are formed inside of the Earth. There are two types of Metamorphic rocks. Foliated rocks and non-folliated rocks are the two main types.
- Foliated rocks are formed with the alignment of minerals.
- Non-foliated rocks are formed without any special alignment.
Examples of Different Rocks
Pegmatite
- Pegmatite forms inside of the volcano slowly, so they have larger crystals. Therefore, pegmatite is intrusively formed.
- The crystal size of this rock is 10 mm or larger with a very coarse texture.
- Pegmatite is non-vesicular.
- This rock has a lighter color, low density and low composition.
- Potassium Feldspar- 25%
Plagioclase Feldspar- 20%
Biotite- 10%
Amphibole- 7%
Bituminous Coal
- Bituminous coal is organically formed.
- The size of the grains are microscopic to very coarse and it is bioclastic.
- The composition of bituminous coal is carbon.
- Compacted plant remains.
Phyllite
- Phyllite is foliated with a mineral alignment.
- The grain size is medium to coarse.
- Composition: Mica, Quartz, Feldspar, Amphibole and Garnet.
- the type of metamorphism is regional (heat and pressure increases).
- Foliation surfaces shiny from microscopic mica crystals.
The Rock Cycle
The Rock Cycle is a process in which rocks go through just to become a different type of rock. A rock can become the same rock again if it goes through the whole process.