These sedimentary rocks originated as loose grains of rock materials, predominantly quartz but occasionally feldspars or some other mineral. These materials, eroded from older rocks, have been sorted and deposited by the physical action of water and sometimes wind to form beds. Consolidation ensues over millions of years by processes similar to those responsible for the formation of limestone. The cement of sandstone may be rich in various minerals: silica, iron, calcium carbonate, all of which contribute to the final colour and characteristics of the sandstone. Sandstone beds also possess natural joining systems.
The toughness of sandstone depends mostly on the nature of the cementing material. The colour of the sandstone is often determined largely by the cementing material, iron oxides causing red or reddish brown sandstone, and the other materials producing white, yellow etc
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