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post in: LifeStyle, News Date:30 Nov 2012, 18:59 views:1131
Rock or stone is a natural substance, a solid aggregate of one or more minerals or mineraloids. For example, granite, a common rock, is a combination of the minerals quartz, feldspar and biotite. The Earth's outer solid layer, the lithosphere, is made of rock.
Rock has been used by mankind throughout history. The minerals and metals found in rocks have been essential to human civilization.1. Three major groups of rocks are defined: igneous, sedimentary, and metamorphic.
The scientific study of rocks is called petrology, which is an essential component of geology. Rocks are geologically classified according to characteristics such as mineral and chemical composition, permeability, the texture of the constituent particles, and particle size. These physical properties are the end result of the processes that formed the rocks.3 Over the course of time, rocks can transform from one type into another, as described by the geological model called the rock cycle.
These events produce three general classes of rock: igneous, sedimentary, and metamorphic. About.7 of the Earth's crust by volume consists of igneous rocks; making it the most plentiful category. Of these, 66 are basalts and gabbros, 16 are granite, and 17 granodiorites and diorites.
Only.6 are syenites and.3 peridotites and dunites. The oceanic crust is 99 basalt, which is an igneous rock of mafic composition.
Granites and similar rocks, known as meta-granitoids, form much of the continental crust.5 Over 700 types of igneous rocks have been described, most of them having formed beneath the surface of Earth's crust. These have diverse properties, depending on their composition and the temperature and pressure conditions in which they were formed.
Metamorphic rocks are formed by subjecting any rock typesedimentary rock, igneous rock or another glad older metamorphic rockto different temperature and pressure conditions than those in which the original rock was formed. This process is called metamorphism; meaning to "change in form". The result is a profound change in physical properties and chemistry of the stone.
The original rock, known as the protolith, transforms into other mineral types or other forms of the same minerals, by recrystallization.3 The temperatures and pressures required for this process are always higher than those found at the Earth's surface: temperatures greater than 150 to 200. Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or (coal) seam.
This term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock salt and potash. Mining is required to obtain any material that cannot be grown through agricultural processes, or created artificially in a laboratory or factory.