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Facts about Rocks or Stones for Kids


  • In geology, rock or stone is a naturally occurring solid aggregate of one or more minerals or mineraloids.
  • For example, the common rock granite is a combination of the quartz, feldspar and biotite minerals.
  • Rocks have been used by mankind throughout history.
  • At a granular level, rocks are composed of grains of minerals, which, in turn, are homogeneous solids formed from a chemical compound that is arranged in an orderly manner.
  • Many rocks contain silica (SiO2); a compound of silicon and oxygen that forms 74.3% of the Earth’s crust.
  • Rocks are geologically classified according to characteristics such as mineral and chemical composition, permeability, the texture of the constituent particles, and particle size.
  • Over the course of time, rocks can transform from one type into another, as described by the geological model called the rock cycle.
  • Typically, the melting of rocks is caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition.
  • Igneous rocks are divided into two main categories: plutonic rock and volcanic.
  • Sedimentary rocks are formed at the earth’s surface by the accumulation and cementation of fragments of earlier rocks, minerals, and organisms or as chemical precipitates and organic growths in water (sedimentation).
  • This process causes clastic sediments (pieces of rock) or organic particles (detritus) to settle and accumulate, or for minerals to chemically precipitate (evaporite) from a solution.
  • Before being deposited, sediments are formed by weathering or earlier rocks by erosion in a source area, and then transported to the place of deposition by water, wind, ice, mass movement or glaciers (agents of denudation).
  • Mud rocks comprise 65% (mudstone, shale and siltstone); sandstones 20 to 25% and carbonate rocks 10 to 15% (limestone and dolostone).
  • About 7.9% of the crust by volume is composed of sedimentary rocks, with 82% of those being shales, while the remainder consist of limestone (6%), sandstone and arkoses (12%).
  • A small fraction of sedimentary rocks deposited on steep slopes will show cross bedding where one layer stops abruptly along an interface where another layer eroded the first as it was laid atop the first.
  • Pressure metamorphism occurs when sediments are buried deep under the ground; pressure is dominant and temperature plays a smaller role.
  • Schists are foliated rocks that are primarily composed of lamellar minerals such as micas.
  • The mining of rocks for their metal ore content has been one of the most important factors of human advancement, which has progressed at different rates in different places in part because of the kind of metals available from the rocks of a region.
  • Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or (coal) seam.