BY: Thomas Fasano
What are rocks?
Rocks are composed of minerals. They are classified by how they were formed (their origin).
- Igneous rocks are formed by cooling and crystalization of molten rock (Magma, Lava). When an igneous rock solidifies it forms crystals. The longer it takes for the rock to cool the larger the crystals are.
- There are two types of igneous rocks.
- Intrusive igneous rocks are rocks that crystalizes slowly inside the earth's crust.
- Extrusive igneous rocks are rocks that crystalize quickly at the earth's surface.
- Most sedimentary rocks are composed primarily of the weathered (broken) remains of other rocks.
- There are three types of sedimentary rocks.
- Clastic sedimentary rocks are made of different sized particles cemented together.
- Bioclastic sedimentary rocks are formed by the accumulation of plant and animal remains (fragments) containing shells or plant material.
- Crystalline sedimentary rocks are deposited with chemicals in sea water precipitate and fall to the ocean bottom.
- Metamorphic rocks form when other rocks are exposed to heat and/or pressure without melting. There are two types of metamorphism.
- Regional Metamorphism is large masses of rock changed by deep burial within the earth.
- Contact Metamorphism is chemical and physical change to a rock caused by nearby intrusion or extrusion of molten rock.
Gabbro is an intrusive Igneous rock. It is formed inside a volcano. It's texture is course and is non-vesicular. The minerals it is composed of are Plagioclase Feldspar, Biotite, Amphibole, Pryoxene, and Olivine. Gabbro is a darker color and has a high density.
Limestone is a chemically and/or organically formed Sedimentary rock. It's texture is crystalline or bioclastic and has a grain size of microscopic to very coarse. Limestone is composed of Calcite.
Marble is a Metamorphic rock. It's texture is Non-Foliated and has a grain size of fine to coarse. Marble is composed of Calcite and/or Dolomite. Marbles type of Metamorphism is regional or contact.