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Sandstone

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Sandstone is a sedimentary rock and one of the most common types of sedimentary rock and is found in sedimentary basins throughout the world. It is composed of sand-size grains rock fragment, mineral and organic material. Sand-size particles range in size from 1/16 millimeter to 2 millimeters in diameter. Also it have cementing material binds the sand grains together and may contain a matrix of silt- or clay-size particles that occupy the spaces between the sand grains.

Quartz-bearing sandstone can be changed into quartzite through metamorphism, usually related to tectonic compression within orogenic belts.

Texture: Clastic (only noticeable with a microscope).

Grain size: 0.06 – 2mm; clasts visible to the naked eye, often identifiable.

Hardness: Variable, soft to hard, dependent on clast and cement composition.

Colour: Variable through grey, yellow, red to white reflecting the variation in mineral content and cement.

Clasts: Dominantly quartz and feldspar ( orthoclase, plagioclase) with lithic clasts and varying minor amounts of other minerals.

Other features: Gritty to touch (like sandpaper).

Minerals: Quartz or feldspar (both silicates)

Sandstone Composition

Chemical Composition of sandstone usually quartz framework grains are the dominant mineral in clastic sedimentary rocks. Because of they have exceptional physical properties such as hardness and chemical stability.Physcial properties of these quartz grains survive multiple recycling events and also allowing the grains to display some degree of rounding. Quartz grains evolve from plutonic rock, which are felsic in origin and also from older sandstones that have been recycled. Second most abundant mineral is feldspathic framework grains.

Feldspar can be seperate into two subdibision. They are alkali feldspars and plagioclase feldspars. Feldspars minerals is distinguished under a petrographic microscope.

Alkali feldspar is a group of minerals in which the chemical composition of the mineral can range from KAlSi3O8 to NaAlSi3O8, this represents a complete solid solution.

Plagioclase feldspar is a complex group of solid solution minerals that range in composition from NaAlSi3O8 to CaAl2Si2O8.

Photomicrograph of a volcanic sand grain; upper picture is plane-polarised light, bottom picture is cross-polarised light, scale box at left-centre is 0.25 millimetre. This type of grain would be a main component of a lithic sandstone.

Lithic framework grains are pieces of ancient source rock that have yet to weather away to individual mineral grains, called lithic fragments or clasts. Lithic fragments can be any fine-grained or coarse-grained igneous, metamorphic, or sedimentary rock, although the most common lithic fragments found in sedimentary rocks are clasts of volcanic rocks.

Accessory minerals are small percentage of the grain in a sandstone.Common accessory minerals include micas (muscovite and biotite), olivine, pyroxene, and corundum. Many of these accessory grains are more density to silicates minerals in the rocks. These heavy minerals moere durability to weathering and can be used as an indicator of sandstone maturity through the ZTR index.

Common heavy minerals include zircon, tourmaline, rutile (hence ZTR), garnet, magnetite, or other dense, resistant minerals derived from the source rock.

Matrix

Matrix is present within fractured pore space between the framework grains. This pore space can be seperate into the two class. They are Arenites and Wackes. Arenites are texturally clean sandstones that are free of or have very little matrix. Wackes are texturally dirty sandstones that have a significant amount of matrix.

Cement

Cement is binds the siliciclastic framework grains together. Cement is a secondary deposition minerals after during burial of sandstone.These cementing materials may be either silicate minerals or non-silicate minerals, such as calcite. Silica cement can consist of either quartz or opal minerals. Calcite cement is the most common carbonate cement. Calcite cement is an assortment of smaller calcite crystals. Other minerals that act as cements include: hematite, limonite, feldspars, anhydrite, gypsum, barite, clay minerals, and zeolite minerals.

Sandstone Formation

Formation of the sandstones are cemented grains that may either be fragments of a pre-existing rock or be mono-minerallic crystals. The cements binding these grains together are typically calcite, clays, and silica. Grain sizes in sands are defined (in geology) within the range of 0.0625 mm to 2 mm (0.0025–0.08 inches). Clays and sediments with smaller grain sizes not visible with the naked eye, including siltstones and shales, are typically called argillaceous sediments; rocks with larger grain sizes, including breccias and conglomerates, are termed rudaceous sediments. The most common cementing materials are silica and calcium carbonate, which are often derived either from dissolution or from alteration of the sand after it was buried. Colors will usually be tan or yellow (from a blend of the clear quartz with the dark amber feldspar content of the sand). The environment where it is deposited is crucial in determining the characteristics of the resulting sandstone, which, in finer detail, include its grain size, sorting, and composition and, in more general detail, include the rock geometry and sedimentary structures. Principal environments of deposition may be split between terrestrial and marine, as illustrated by the following broad groupings:

Terrestrial environments

  • Rivers (levees, point bars, channel sands)
  • Alluvial fans
  • Glacial outwash
  • Lakes
  • Deserts (sand dunes and ergs)

Marine environments

  • Deltas
  • Beach and shoreface sands
  • Tidal flats
  • Offshore bars and sand waves
  • Storm deposits (tempestites)
  • Turbidites (submarine channels and fans)

Where is the Sandstone found?

Sandstone can be found to many place to deposits across the World. In the USA, there are four main sandstone deposits that can be found in Virginia, Wisconsin, Michigan and New York. Aquia Creek Sandstone, found in Stafford County Virginia, has been used in many of Washington’s prominent government buildings, including the White House. There are at least 8 varieties of sandstone to be found in South Africa, but many of the quarries in this country have since closed down. Europe is home to most of the sandstone deposits of the world, with countries such as Switzerland, Germany and France holding the bulk of them. Germany, in fact, lays claim on having the most deposits in the entire world with around 64 varieties of the stone all being found in different areas.

Sandstone Uses

  • Sandstone was used domestic construction and housewares  even in prehistoric times.
  • Sandstone was a popular building material from ancient times. It is relatively soft, making it easy to carve. It has been widely used around the world in constructing temples, homes, and other buildings.
  • It has also been used for artistic purposes to create ornamental fountains and statues.
  • Some sandstones are resistant to weathering, yet are easy to work. This makes sandstone a common building and paving material including in asphalt concrete.
  • Because of the hardness of individual grains, uniformity of grain size and friability of their structure, some types of sandstone are excellent materials from which to make grindstones, for sharpening blades and other implements.

Conclusion

  • Sandstone is a versatile building structure and has been used to construct buildings, statues, and fountains.
  • Sandstone is popular in constructing buildings because it is resistant to weathering.
  • Sandstone can form under the sea or on land.
  • It is common to find natural gas in sandstone because sandstone is porous and traps it.
  • Grindstone wheels, which are used for sharpening, are made of sandstone.
  • Sandstone can be categorized into three groups: arkosic, quartzose, and argillaceous.
  • Because sandstone is porous it can serve as a filter in nature by filtering out pollutants from running water.
  • Sandstone is often broken down and used as industrial sand.
  • Groundwater can be transported by underground sandstone.
  • Underground sandstone is drilled and pumped as a good source for groundwater.
  • Sandstone rock can take thousands of years to form.

References

Cite this article as: Geology Science. (2019). Sandstone. [online] Available at: http://geologyscience.com/rocks/sandstone/ [12th November 2019 ]
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