Monday, 16 March 2015

Sandstone

Sandstone

Sandstone is a sedimentary rock that is composed of sand size grain particles such as minerals, rock fragments or organic material. Sandstone is the most common rock type found throughout the world. It has large pore spaces and is often bind together by cementing material or clay and silt as a matrix. Sandstone is often mined to use as a construction material e.g. building block of a wall or as a raw material for other manufacturing. Due to the large pore spaces of sandstone, it is interconnected thus has permeability that allows liquid and gas to pass through it. For this reason sandstone mostly occur as aquifer for ground water and even a reservoir for oil and gas.

Sandstone weathering and transport

Sandstone comprises of particles range from 1/16 to 2 millimetre. Sandstone is derived from pre-existing rock by their weathering. Rock is weathered and break into fine sand size particles which are then carried by transporting agent as water, wind or ice. The particles is transported to the site of deposition and during this transport it is subjected to chemical and physical weathering. When sand deposits near the source rock, the properties will be resembled to that of the source rock but in large time and space difference in transport, the sand particle which is durable will be highly modified and those less resistant can be reduced in size or completely destroyed.
The composition of the source rock matters much for example if the source rock is granite it will contain minerals of hornblende, orthoclase, biotite and quartz. Orthoclase and quartz are more resistant due to their high hardness so they have great chance of survival but biotite and hornblende are less resistible to chemical and physical weathering to they will be destroyed. 

Sand grain types

The grains of sandstone can comprise of minerals, rock or organic matter depend upon the source rock. The sandstone can be classified according to the Folk's classification. If a sandstone has above 90% quartz so it will be quartz arenite. If it has more feldspar it will be arkose and will increasing lithics and feldspar, changes from arkose to lithic arkose and then to feldspathic litharenite. Same is the case with quartz and lithic fragments.

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