rocks

Types of rocks

1. Igneous rock

Igneous rock (derived from the Latin word 'Igneus' meaning of fire, from "Ignis" meaning fire) is one of the three main rock types (the others being sedimentary nd metamorphic rock). Igneous rock is formed by magma (molten rock) cooling and becoming solid. Igneous rock may from with or without crystallization, either below the surface as intrusive rocks or on the surface as extrusive rocks. This magma can be derived from partial melts of pre-existing rocks in either a planet's mantle or crust. Typically, the melting caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition. Over 700 types of igneous rocks have been described, mos of them having formed beneath the surface of Earth's crust. These have diverse properties, depending on their composition and how they were formed. EXAMPLE :

2. sedimentary

sedimentary rock is a type of rock that is formed by sedimentation of material at the Earth's surface and within bodies of water. sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to percipitate from a solution. Particles that form a sedimentary rock by accumulating are called sediment. Before being deposited, sediment was formed by weathering and erosion in a source area, and then transported to the place of deposition by water, wind, mass movement of glaciers. The sedimentary rock cover of the continents of the Earth's crust is extensive, but the totla contribution of sedimentary rocks is estimated to be only 5%of the total volume of the crust. Sedimentary rocks are only a thin veneer over a crust consisting mainly of igneous and metamorphic rocks.

3.metamorphic rocks

metamorphic rock**​** is the result of the transformation of an existing rock type, the //protolith//, in a process called metamorphism, which means "change in form". The protolith objected to heat and pressure (temperatures greater than 150 to 200 °C and pressures of 1500 bars) causing profound physical and/or chemical change. The protolith may be sedimentary rock, igneous rock or another older metamorphic rock. Metamorphic rocks make up a large part of the Earth's crust and are classified by texture and by chemical and mineral assemblage (metamorphic facies). They may be formed simply by being deep beneath the Earth's surface, subjected to high temperatures and the great pressure of the rock layers above it. They can form from tectonic processes such as continental collisions, which cause horizontal pressure, friction and distortion. They are also formed when rock is heated up by the intrusion of hot molten rock called magma from the Earth's [[interior (topology)|]. The study of metamorphic rocks (now exposed at the Earth's surface following erosion and uplift) provides us with very valuable information about the temperatures and pressures that occur at great depths within the Earth's crust.