What is a rock?
Earth’s crust is made up of various types of rocks. When one or more minerals are mixed together, they aggregately called a rock. So, rock is an aggregate of one or more minerals.
The rock can be composed of one mineral or more than one mineral. For example, quartzite rock almost made up of mineral quartz. Other hand, granite rock is composed of four minerals quartz, feldspar, mica, and hornblende.
The rocks can be hard or soft. for example, granite is hard rock and clay is soft rock.
It is the most common mineral of the rocks. About half of the earth’s crust contains this mineral. Feldspar is the various aluminosilicate of potassium, sodium, calcium, and barium.
Quartz is the second most found mineral in the earth’s crust. The word quartz derives from the German word ‘Quartz’ which means ‘hard’. It’s the main ingredient of soil and granite.
Basalt, Gabbro, Dolerite, etc rocks are composed of pyroxene group. Pyroxene crystals are prismatic in shape. Rocks made of pyroxene minerals are called pyroxenes.
The amphibole consists of aluminum, silica, calcium, iron, and magnesium. Amphibole has structure and properties similar to pyroxene. Pyroxene and amphibole recognized by optical properties as they show different optical characteristics.
Mica can be cut into a very thin layer. It’s mostly found in igneous and metamorphic rocks. Mica is a very complex compound of silicate and it’s unaffected by acid.
Olivine is a magnesium iron silicate. Olivine is found all over the earth and also found in a meteorite.
In addition to these minerals, bauxite, barite, calcite, chlorite, and magnetite are also found in small quantities in the earth’s crust.
Three types of rocks
There are three types of rocks based on how the rock is formed: igneous rock, sedimentary rock, and metamorphic rock.
1. Igneous rock
Igneous rocks are made up of magma, so it’s also called primary rocks. When hot magma comes out of the earth’s crust, it’s referred to as lava. Igneous rocks are formed by cooling, crystallization, and solidification of hot magma and lava.
The rocks that are formed below the surface of the earth are called intrusive igneous rocks. The extrusive igneous rock is another type of igneous rock that is formed when magma reaches the Earth’s surface and cools quickly.
Igneous rock does not contain fossils, as they are formed from magma and there is no possibility of life in magma. The igneous rocks can be found in crystals. The igneous rocks are hard and solid because they are formed of magma.
Granite, basalt, and gabbro are the most commonly found igneous rocks.
2. Sedimentary rocks
Igneous rocks are often exposed to natural factors and undergo the process of weathering. As a result, igneous rocks break down into small rocks, soil, and dust, which are called sediment. Now, the sediment is transported to another place due to erosion. Most of the erosion caused by water, which drains the sediments to the low-lying area.
Now, here sediments accumulate. Then by the lithification process, these accumulated sediments become sedimentary rocks. The lithification process comprises two different processes: compaction and cementation.
The various known sedimentary rocks are clay, sandstone, limestone, coal, salt rock, gypsum, and dolomite.
The sedimentary or igneous rocks get buried deep in the earth. Here, rocks experience the increased pressure, heat, and chemical process that change the structure of the rocks. This process called metamorphism. Due to metamorphism igneous or sedimentary rocks become a metamorphic rock. For example, when a sandstone rock undergoes the process of metamorphism, it’s become a metamorphic rock called quartzite.
Quartzite, graphite, marble, and gneiss are some of the metamorphic rocks.
The rock cycle is a continuous process, in which old rocks are deformed and new rocks are formed.
The cooling, crystallization, and solidification of magma form the igneous rock. Due to weathering, the igneous rocks are continuously broken into sediments. These sediments are moved away by erosion. Then sediments deposited to new areas. And then by lithification, sediments harden into a rock called sedimentary rocks. The sedimentary and igneous rocks undergo the process of metamorphism and become metamorphic rock. With further burial and heating, the metamorphic rocks being melt and become magma. Now, the magma cools down and becomes igneous rock by crystallization and solidification. Again due to weathering, erosion, deposition, and lithification, the igneous rock transformed into sedimentary rocks. And this rock cycle continuously goes on and on.