Rocks
By Meagan Garcia
What is a rock?
A rock is composed of minerals. Rocks are classified by how they were formed or by their origin. There are three types of rocks Igneous, Sedimentary and, Metamorphic.
Igneous Rocks
Igneous rocks are formed by melting and solidification of molten rocks usually at 600 - 1000 Celsius. When it solidifies it forms crystals the cooling rate determines the crystal size with in an igneous rock. Igneous rocks are formed by a volcano. Fast cool which usually takes place e outside of (extrusive) the volcano does not provide time for the crystals to form so the crystals are small. Slow cooling does provide for the crystals to form into large crystal because there intrusive in the volcano.
Sedimentary
Sedimentary rocks usually formed by the compaction which adds pressure and cementing of sediments(rock fragmentation).Most sedimentary rocks are composed primarily of broken remains of other rocks. Sedimentary rocks s are commonly found at or near the Earth's surface. Fossils are only found in sedimentary rocks. There are three types of rocks Clastic, Bioclastic and, Crystalline. Clastic is made of different sized particles cemented together. Bioclastic which are formed by the accumulation of plant and animal remains. Crystalline which is deposited when chemicals in seawater fall to the bottom.
Metamorphic
Metamorphic rocks are formed deep within the Earth up to 20 km. They are also formed when other rocks are exposed to heat and/or pressure without melting. There are two different types foliated and nonfoliated.
Basalt
- Extrusive
- Fine
- Non vesicular
- Igneous Rock
- Slow cooling
- Darker,Higher and, Mafic
Siltstone
- Sedimentary Rock
- Clastic
- Silt (.0004-.006)
- inorganic
- very fine grain
Gneiss
- Foliated
- Metamorphic Rock
- Banding
- medium to coarse
- Regional
- Mica, Quartz, Feldspar, Amphibole, Garnet, Pyroxene