Rocks
By: Adrianna Kobyleckyj
Types Of Rocks
Rocks are composed of minerals. They are classified by how they were formed, which is also known as their origin. The three different rock types are called Igneous, Sedimentary, and Metamorphic.
Igneous
Igneous rocks are formed in volcanoes by the process of melting and solidification. There are two main types which are called intrusive and extrusive. Intrusive forms inside the volcano by slowly cooling, and forming larger crystals. Extrusive forms outside the volcano by cooling at a faster rate, and forming smaller crystals.
Sedimentary
Sedimentary rocks form on Earth's surface by the process of cementing and compaction. The three main types of sedimentary rocks are Clastic (Fragmental), Bioclastic (Organic), and Crystalline (Chemical). Clastic is made of different sized particles cemented together. Bioclastic is formed by the accumulation of plant and animal remains containing shells or plant material. Crystalline is formed when deposited chemicals in seawater precipitate and fall to the ocean bottom. Sedimentary rocks are the only type of rock that contain fossils.
Metamorphic
Metamorphic rocks are formed deep in the ground by undergoing the process of heat and pressure. The two types of metamorphic rocks are called Foliated and Non-Foliated. Foliation is when there is an alignment of minerals in the rock. Also, metamorphic rocks can have banding which is a type of foliation that has wavy colored stripes.
Examples Of Different Rocks
Rhyolite
Rhyolite is a type of extrusive igneous rock. This means that it cools at a faster rate, and forms small crystals. It has a fine grained texture which is less than 1mm. Also, it is non-vesicular. Rhyolite is a light colored rock and has a low density. It's composition is felsic which means it is rich in Silicon and Aluminum. In Rhyolite, there is 20% of Potassium Feldspar, 40% of Quartz, 23% of Plagioclase Feldspar, 10% of Biotite, and 10% of Amphibole.
Conglomerate
Conglomerate is a type of inorganic sedimentary rock. It has a Clastic (fragmental), and usually has a grain size of pebbles, cobbles, and/or boulders embedded in sand. Conglomerate mostly contains Quartz, Feldspar, and clay minerals. It also may contain fragments of other rocks and minerals. It usually has rounded fragments.
Slate
Slate is a type of foliated metamorphic rock. This means it has mineral alignment. Also, it is fine grained. The composition of Slate include only Mica. It is formed by Regional Metamorphism which means both heat and pressure are increased. Lastly, it is a low-grade metamorphism of shale.
The Rock Cycle
The Rock Cycle is a model showing how rocks and sediments change over time.