Rock by Handsome Wu

Different types of Rocks:affraid:
In geology, rock is a naturally occurring aggregate of minerals and/or mineraloids.
The Earth's outer solid layer, the ‘lithosphere’, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic. The scientific study of rocks is called ‘petrology’
Igneous rock (etymology from Latin ignis, fire) is one of the three main rock types (the others being sedimentary and metamorphic rock). Igneous rocks are formed by solidification of cooled magma (molten rock). They may form with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. This magma can be derived from partial melts of pre-existing rocks in either the Earth's mantle or crust. Typically, the melting is caused by one or more of the following processes — an increase in temperature, a decrease in pressure, or a change in composition. Over 700 types of igneous rocks have been described, most of them formed beneath the surface of the Earth's crust. These have diverse properties, depending on their composition and how they were formed.
Sedimentary rock is one of the three main rock types (the others being igneous and metamorphic rock). Rock formed from sediments covers 75-80% of the Earth's land area, and includes common types such as chalk, limestone, dolomite, sandstone, conglomerate and shale.[1]
Sedimentary rocks are classified by the source of their sediments, and are produced by one or more of:
• clastic rock formed from fragments broken off from parent rock, by
o weathering in situ or
o erosion by water, ice or wind, followed by transportation of sediments, often in suspension, to the place of deposition;
• biogenic activity; or
• precipitation from solution.
The sediments are then compacted and converted to rock by the process of lithification.
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 is subjected to heat and pressure (temperatures greater than 150 to 200 °C and pressures of 1500 bars[1]) 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. They can be formed by 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.
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.
Some examples of metamorphic rocks are gneiss, slate, marble, schist, and quartzite.