Sandstone

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Sandstone
Sedimentary rock
USDA Mineral Sandstone 93c3955.jpg
Cut slab of sandstone
Composition
Typically quartz and feldspar; lithic fragments are also common. Other minerals may be found in particularly mature sandstone.

Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 2025% of all sedimentary rocks. [1]

Contents

Most sandstone is composed of quartz or feldspar (both silicates) because they are the most resistant minerals to weathering processes at the Earth's surface. Like uncemented sand, sandstone may be any color due to impurities within the minerals, but the most common colors are tan, brown, yellow, red, grey, pink, white, and black. Since sandstone beds often form highly visible cliffs and other topographic features, certain colors of sandstone have been strongly identified with certain regions.

Rock formations that are primarily composed of sandstone usually allow the percolation of water and other fluids and are porous enough to store large quantities, making them valuable aquifers and petroleum reservoirs. [2] [3]

Quartz-bearing sandstone can be changed into quartzite through metamorphism, usually related to tectonic compression within orogenic belts. [4] [5]

Origins

Sandstones are clastic in origin (as opposed to either organic, like chalk and coal, or chemical, like gypsum and jasper). [6] The silicate sand grains from which they form are the product of physical and chemical weathering of bedrock. [7] Weathering and erosion are most rapid in areas of high relief, such as volcanic arcs, areas of continental rifting, and orogenic belts. [8]

Eroded sand is transported by rivers or by the wind from its source areas to depositional environments where tectonics has created accommodation space for sediments to accumulate. Forearc basins tend to accumulate sand rich in lithic grains and plagioclase. Intracontinental basins and grabens along continental margins are also common environments for deposition of sand. [9]

As sediments continue to accumulate in the depositional environment, older sand is buried by younger sediments, and it undergoes diagenesis. This mostly consists of compaction and lithification of the sand. [10] [11] Early stages of diagenesis, described as eogenesis, take place at shallow depths (a few tens of meters) and are characterized by bioturbation and mineralogical changes in the sands, with only slight compaction. [12] The red hematite that gives red bed sandstones their color is likely formed during eogenesis. [13] [14] Deeper burial is accompanied by mesogenesis, during which most of the compaction and lithification takes place. [11]

Compaction takes place as the sand comes under increasing pressure from overlying sediments. Sediment grains move into more compact arrangements, ductile grains (such as mica grains) are deformed, and pore space is reduced. In addition to this physical compaction, chemical compaction may take place via pressure solution. Points of contact between grains are under the greatest strain, and the strained mineral is more soluble than the rest of the grain. As a result, the contact points are dissolved away, allowing the grains to come into closer contact. [11]

Lithification follows closely on compaction, as increased temperatures at depth hasten deposition of cement that binds the grains together. Pressure solution contributes to cementing, as the mineral dissolved from strained contact points is redeposited in the unstrained pore spaces. [11]

Mechanical compaction takes place primarily at depths less than 1,000 meters (3,300 ft). Chemical compaction continues to depths of 2,000 meters (6,600 ft), and most cementation takes place at depths of 2,000–5,000 meters (6,600–16,400 ft). [15]

Unroofing of buried sandstone is accompanied by telogenesis, the third and final stage of diagenesis. [12] As erosion reduces the depth of burial, renewed exposure to meteoric water produces additional changes to the sandstone, such as dissolution of some of the cement to produce secondary porosity. [11]

Components

Framework grains

Paradise Quarry, Sydney, Australia (1)Saunders Quarry-1.jpg
Paradise Quarry, Sydney, Australia
Grus sand and the granitoid from which it is derived GrusSand.JPG
Grus sand and the granitoid from which it is derived

Framework grains are sand-sized (0.0625-to-2-millimeter (0.00246 to 0.07874 in) diameter) detrital fragments that make up the bulk of a sandstone. [16] [17] Most framework grains are composed of quartz or feldspar, which are the common minerals most resistant minerals to weathering processes at the Earth's surface, as seen in the Goldich dissolution series. [18] Framework grains can be classified into several different categories based on their mineral composition:

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 millimeter. This type of grain would be a main component of a lithic sandstone. LvMS-Lvm.jpg
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 millimeter. This type of grain would be a main component of a lithic sandstone.

Matrix

Matrix is very fine material, which is present within interstitial pore space between the framework grains. [1] The nature of the matrix within the interstitial pore space results in a twofold classification:

Cement

Cement is what binds the siliciclastic framework grains together. Cement is a secondary mineral that forms after deposition and during burial of the sandstone. [1] These cementing materials may be either silicate minerals or non-silicate minerals, such as calcite. [1]

Sandstone that becomes depleted of its cement binder through weathering gradually becomes friable and unstable. This process can be somewhat reversed by the application of tetraethyl orthosilicate (Si(OC2H5)4) which will deposit amorphous silicon dioxide between the sand grains. [21] The reaction is as follows.

Si(OC2H5)4 (l) + 2 H2O (l) → SiO2 (s) + 4 C2H5OH (g)

Pore space

Pore space includes the open spaces within a rock or a soil. [22] The pore space in a rock has a direct relationship to the porosity and permeability of the rock. The porosity and permeability are directly influenced by the way the sand grains are packed together. [1]

Types of sandstone

Schematic QFL diagram showing tectonic provinces QFLtriangle.svg
Schematic QFL diagram showing tectonic provinces
Cross-bedding and scour in sandstone of the Logan Formation (Lower Carboniferous) of Jackson County, Ohio Logan Formation Cross Bedding Scour.jpg
Cross-bedding and scour in sandstone of the Logan Formation (Lower Carboniferous) of Jackson County, Ohio
Red sandstone interior of Lower Antelope Canyon, Arizona, worn smooth by erosion from flash flooding over thousands of years Lower antelope 2 md.jpg
Red sandstone interior of Lower Antelope Canyon, Arizona, worn smooth by erosion from flash flooding over thousands of years

Sandstones are typically classified by point-counting a thin section using a method like the Gazzi-Dickinson Method. This yields the relative percentages of quartz, feldspar, and lithic grains and the amount of clay matrix. The composition of a sandstone can provide important information on the genesis of the sediments when used with a triangular Quartz, Feldspar, Lithic fragment (QFL diagrams). However, geologist have not been able to agree on a set of boundaries separating regions of the QFL triangle. [1]

Visual aids are diagrams that allow geologists to interpret different characteristics of a sandstone. For example, a QFL chart can be marked with a provenance model that shows the likely tectonic origin of sandstones with various compositions of framework grains. Likewise, the stage of textural maturity chart illustrates the different stages that a sandstone goes through as the degree of kinetic processing of the sediments increases. [23]

Dott's classification scheme

Dott's (1964) sandstone classification scheme is one of many such schemes used by geologists for classifying sandstones. Dott's scheme is a modification of Gilbert's classification of silicate sandstones, and it incorporates R.L. Folk's dual textural and compositional maturity concepts into one classification system. [25] The philosophy behind combining Gilbert's and R. L. Folk's schemes is that it is better able to "portray the continuous nature of textural variation from mudstone to arenite and from stable to unstable grain composition". [25] Dott's classification scheme is based on the mineralogy of framework grains, and on the type of matrix present in between the framework grains.

In this specific classification scheme, Dott has set the boundary between arenite and wackes at 15% matrix. In addition, Dott also breaks up the different types of framework grains that can be present in a sandstone into three major categories: quartz, feldspar, and lithic grains. [1]

Quartzite

When sandstone is subjected to the great heat and pressure associated with regional metamorphism, the individual quartz grains recrystallize, along with the former cementing material, to form the metamorphic rock called quartzite. Most or all of the original texture and sedimentary structures of the sandstone are erased by the metamorphism. [4] The grains are so tightly interlocked that when the rock is broken, it fractures through the grains to form an irregular or conchoidal fracture. [26]

Geologists had recognized by 1941 that some rocks show the macroscopic characteristics of quartzite, even though they have not undergone metamorphism at high pressure and temperature. These rocks have been subject only to the much lower temperatures and pressures associated with diagenesis of sedimentary rock, but diagenesis has cemented the rock so thoroughly that microscopic examination is necessary to distinguish it from metamorphic quartzite. The term orthoquartzite is used to distinguish such sedimentary rock from metaquartzite produced by metamorphism. By extension, the term orthoquartzite has occasionally been more generally applied to any quartz-cemented quartz arenite. Orthoquartzite (in the narrow sense) is often 99% SiO2 with only very minor amounts of iron oxide and trace resistant minerals such as zircon, rutile and magnetite. Although few fossils are normally present, the original texture and sedimentary structures are preserved. [27] [28]

The typical distinction between a true orthoquartzite and an ordinary quartz sandstone is that an orthoquartzite is so highly cemented that it will fracture across grains, not around them. [29] This is a distinction that can be recognized in the field. In turn, the distinction between an orthoquartzite and a metaquartzite is the onset of recrystallization of existing grains. The dividing line may be placed at the point where strained quartz grains begin to be replaced by new, unstrained, small quartz grains, producing a mortar texture that can be identified in thin sections under a polarizing microscope. With increasing grade of metamorphism, further recrystallization produces foam texture, characterized by polygonal grains meeting at triple junctions, and then porphyroblastic texture, characterized by coarse, irregular grains, including some larger grains (porphyroblasts.) [26]

Uses

The Main Quadrangle of the University of Sydney, a so-called sandstone university SydneyUniversity MainBuilding Panorama.jpg
The Main Quadrangle of the University of Sydney, a so-called sandstone university
Sandstone statue Maria Immaculata by Fidelis Sporer, around 1770, in Freiburg, Germany MariaImmaculatal Augustiner.jpg
Sandstone statue Maria Immaculata by Fidelis Sporer, around 1770, in Freiburg, Germany
17,000 yr old sandstone oil lamp discovered at the caves of Lascaux, France Lampe a graisse - Lascaux.jpg
17,000 yr old sandstone oil lamp discovered at the caves of Lascaux, France

Sandstone has been used since prehistoric times for construction, [30] [31] decorative art works [32] and tools. [33] It has been widely employed around the world in constructing temples, [34] churches, [34] homes and other buildings, and in civil engineering. [35]

Although its resistance to weathering varies, sandstone is easy to work. That makes it a common building and paving material, including in asphalt concrete. However, some types that have been used in the past, such as the Collyhurst sandstone used in North West England, have had poor long-term weather resistance, necessitating repair and replacement in older buildings. [36] 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. [37] Non-friable sandstone can be used to make grindstones for grinding grain, e.g., gritstone.

A type of pure quartz sandstone, orthoquartzite, with more of 90–95 percent of quartz, [38] has been proposed for nomination to the Global Heritage Stone Resource. [39] In some regions of Argentina, the orthoquartzite-stoned facade is one of the main features of the Mar del Plata style bungalows. [39]

See also

Notes

  1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 Boggs, Sam (2006). Principles of sedimentology and stratigraphy (4th ed.). Upper Saddle River, N.J.: Pearson Prentice Hall. pp. 119–135. ISBN   0131547283.
  2. Swanson, Susan K.; Bahr, Jean M.; Bradbury, Kenneth R.; Anderson, Kristin M. (February 2006). "Evidence for preferential flow through sandstone aquifers in Southern Wisconsin". Sedimentary Geology. 184 (3–4): 331–342. Bibcode:2006SedG..184..331S. doi:10.1016/j.sedgeo.2005.11.008.
  3. Bjørlykke, Knut; Jahren, Jens (2010). "Sandstones and Sandstone Reservoirs". Petroleum Geoscience: 113–140. doi:10.1007/978-3-642-02332-3_4. ISBN   978-3-642-02331-6.
  4. 1 2 Marshak, Stephen. Essentials of Geology (3rd ed.). p. 182.
  5. Powell, Darryl. "Quartzite". Mineral Information Institute. Archived from the original on 2009-03-02. Retrieved 2009-09-09.
  6. 1 2 "A Basic Sedimentary Rock Classification", L.S. Fichter, Department of Geology/Environmental Science, James Madison University (JMU), Harrisonburg, Virginia, October 2000, JMU-sed-classif (accessed: March 2009): separates clastic, chemical & biochemical (organic).
  7. Leeder, M. R. (2011). Sedimentology and sedimentary basins : from turbulence to tectonics (2nd ed.). Chichester, West Sussex, UK: Wiley-Blackwell. pp. 3–28. ISBN   9781405177832.
  8. Blatt, Harvey; Tracy, Robert J. (1996). Petrology : igneous, sedimentary, and metamorphic (2nd ed.). New York: W.H. Freeman. pp. 241–242, 258–260. ISBN   0716724383.
  9. Blatt and Tracy 1996, pp. 220-227
  10. Blatt and Tracy 1996, pp. 265-280
  11. 1 2 3 4 5 Boggs 2006, pp. 147-154
  12. 1 2 Choquette, P.W.; Pray, L.C. (1970). "Geologic Nomenclature and Classification of Porosity in Sedimentary Carbonates". AAPG Bulletin. 54. doi:10.1306/5D25C98B-16C1-11D7-8645000102C1865D.
  13. Walker, Theodore R.; Waugh, Brian; Grone, Anthony J. (1 January 1978). "Diagenesis in first-cycle desert alluvium of Cenozoic age, southwestern United States and northwestern Mexico". GSA Bulletin. 89 (1): 19–32. Bibcode:1978GSAB...89...19W. doi:10.1130/0016-7606(1978)89<19:DIFDAO>2.0.CO;2.
  14. Boggs 2006, p. 148
  15. Stone, W. Naylor; Siever, Naylor (1996). "Quantifying compaction, pressure solution and quartz cementation in moderately-and deeply-buried quartzose sandstones from the Greater Green River Basin, Wyoming". Special Publications of SEPM. Retrieved 2 October 2020.
  16. Dorrik A. V. Stow (2005). Sedimentary Rocks in the Field: A Colour Guide. Manson Publishing. ISBN   978-1-874545-69-9 . Retrieved 11 May 2012.
  17. 1 2 Francis John Pettijohn; Paul Edwin Potter; Raymond Siever (1987). Sand and Sandstone. Springer. ISBN   978-0-387-96350-1 . Retrieved 11 May 2012.
  18. Prothero & Schwab, Donald R. & Fred (1996). Sedimentary Geology. W. H. Freeman. p. 24. ISBN   0-7167-2726-9.
  19. 1 2 Prothero, D. (2004). Sedimentary Geology. New York, NN: W.H. Freeman and Company
  20. Prothero, D. R. and Schwab, F., 1996, Sedimentary Geology, p. 460, ISBN   0-7167-2726-9
  21. Zárraga, Ramón; Alvarez-Gasca, Dolores E.; Cervantes, Jorge (1 September 2002). "Solvent effect on TEOS film formation in the sandstone consolidation process". Silicon Chemistry. 1 (5): 397–402. doi:10.1023/B:SILC.0000025602.64965.e7. S2CID   93736643.
  22. 1 2 3 Jackson, J. (1997). Glossary of Geology. Alexandria, VA: American Geological Institute ISBN   3-540-27951-2
  23. Boggs 2006, pp. 130–131.
  24. Carozzi, A. (1993). Sedimentary petrography. Englewood Cliffs, NJ: Prentice-Hall ISBN   0-13-799438-9
  25. 1 2 Robert H. Dott (1964). "Wacke, greywacke and matrix; what approach to immature sandstone classification?". SEPM Journal of Sedimentary Research. 34 (3): 625–32. doi:10.1306/74D71109-2B21-11D7-8648000102C1865D.
  26. 1 2 Howard, Jeffrey L. (November 2005). "The Quartzite Problem Revisited". The Journal of Geology. 113 (6): 707–713. Bibcode:2005JG....113..707H. doi:10.1086/449328. S2CID   128463511.
  27. Ireland, H. A. (1974). "Query: Orthoquartzite????". Journal of Sedimentary Petrology. 44 (1): 264–265. doi:10.1306/74D729F0-2B21-11D7-8648000102C1865D.
  28. Allaby, Michael (2013). A dictionary of geology and earth sciences (Fourth ed.). Oxford: Oxford University Press. ISBN   9780199653065.
  29. Jackson, Julia A., ed. (1997). Glossary of geology (Fourth ed.). Alexandria, Virginia: American Geological Institute. p. 525. ISBN   0922152349.
  30. Applegate, Alex; Zedeño, Nieves (2001). "Site E-92-8: A Late Prehistoric C-Group Component at Nabta Playa". Holocene Settlement of the Egyptian Sahara: 529–533. doi:10.1007/978-1-4615-0653-9_19. ISBN   978-1-4613-5178-8.
  31. Royden, Mike. "The Calderstones". Mike Royden. Archived from the original on 2008-07-25. Retrieved 2009-07-20.
  32. Bahn, Paul G. (1998). The Cambridge illustrated history of prehistoric art. Cambridge, U.K.: New York. p. 84. ISBN   978-0521454735.
  33. Smith, Kevin N.; Vellanoweth, René L.; Sholts, Sabrina B.; Wärmländer, Sebastian K.T.S. (August 2018). "Residue analysis, use-wear patterns, and replicative studies indicate that sandstone tools were used as reamers when producing shell fishhooks on San Nicolas Island, California". Journal of Archaeological Science: Reports. 20: 502–505. doi:10.1016/j.jasrep.2018.05.011.
  34. 1 2 Saleh, Saleh A.; Helmi, Fatma M.; Kamal, Monir M.; E. El-Banna-a1, Abdel-Fattah (May 1992). "Study and consolidation of sandstone: Temple of Karnak, Luxor, Egypt". Studies in Conservation. 37 (2): 93–104. doi:10.1179/sic.1992.37.2.93.
  35. Grissom, Carol A.; Aloiz, Emily M.; Vicenzi, Edward P.; Livingston, Richard A. (2020). "Seneca sandstone: a heritage stone from the USA". Geological Society, London, Special Publications. 486 (1): 163–176. Bibcode:2020GSLSP.486..163G. doi:10.1144/SP486.4. S2CID   134230768.
  36. Edensor, T. & Drew, I. Building stone in the City of Manchester: St Ann's Church. Sci-eng.mmu.ac.uk. Retrieved on 2012-05-11.
  37. Hannibal, Joseph T. (2020). "Berea sandstone: A heritage stone of international significance from Ohio, USA". Geological Society, London, Special Publications. 486 (1): 177–204. Bibcode:2020GSLSP.486..177H. doi:10.1144/SP486-2019-33. S2CID   210265062.
  38. "Definition of orthoquartzite – mindat.org glossary". www.mindat.org. Retrieved 2015-12-13.
  39. 1 2 Cravero, Fernanda; et al. (8 July 2014). "'Piedra Mar del Plata': An Argentine orthoquartzite worthy of being considered as a 'Global Heritage Stone Resource'" (PDF). Geological Society, London. Archived from the original (PDF) on 9 April 2015. Retrieved 3 April 2015.

Bibliography

Further reading

Related Research Articles

<span class="mw-page-title-main">Shale</span> Fine-grained, clastic sedimentary rock

Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2Si2O5(OH)4) and tiny fragments (silt-sized particles) of other minerals, especially quartz and calcite. Shale is characterized by its tendency to split into thin layers (laminae) less than one centimeter in thickness. This property is called fissility. Shale is the most common sedimentary rock.

<span class="mw-page-title-main">Sedimentary rock</span> Rock formed by the deposition and subsequent cementation of material

Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles to settle in place. The particles that form a sedimentary rock are called sediment, and may be composed of geological detritus (minerals) or biological detritus. The geological detritus originated from weathering and erosion of existing rocks, or from the solidification of molten lava blobs erupted by volcanoes. The geological detritus is transported to the place of deposition by water, wind, ice or mass movement, which are called agents of denudation. Biological detritus was formed by bodies and parts of dead aquatic organisms, as well as their fecal mass, suspended in water and slowly piling up on the floor of water bodies. Sedimentation may also occur as dissolved minerals precipitate from water solution.

Sedimentology encompasses the study of modern sediments such as sand, silt, and clay, and the processes that result in their formation, transport, deposition and diagenesis. Sedimentologists apply their understanding of modern processes to interpret geologic history through observations of sedimentary rocks and sedimentary structures.

<span class="mw-page-title-main">Metamorphism</span> Change of minerals in pre-existing rocks without melting into liquid magma

Metamorphism is the transformation of existing rock to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of 150 to 200 °C, and often also at elevated pressure or in the presence of chemically active fluids, but the rock remains mostly solid during the transformation. Metamorphism is distinct from weathering or diagenesis, which are changes that take place at or just beneath Earth's surface.

<span class="mw-page-title-main">Quartzite</span> Hard, non-foliated metamorphic rock which was originally pure quartz sandstone

Quartzite is a hard, non-foliated metamorphic rock which was originally pure quartz sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to grey, though quartzites often occur in various shades of pink and red due to varying amounts of hematite. Other colors, such as yellow, green, blue and orange, are due to other minerals.

<span class="mw-page-title-main">Lithology</span> Description of its physical characteristics of a rock unit

The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain size, and composition. Lithology may refer to either a detailed description of these characteristics, or a summary of the gross physical character of a rock. Examples of lithologies in the second sense include sandstone, slate, basalt, or limestone.

Petrography is a branch of petrology that focuses on detailed descriptions of rocks. Someone who studies petrography is called a petrographer. The mineral content and the textural relationships within the rock are described in detail. The classification of rocks is based on the information acquired during the petrographic analysis. Petrographic descriptions start with the field notes at the outcrop and include macroscopic description of hand specimens. The most important petrographer's tool is the petrographic microscope. The detailed analysis of minerals by optical mineralogy in thin section and the micro-texture and structure are critical to understanding the origin of the rock.

<span class="mw-page-title-main">Greywacke</span> Hard, dark sandstone with poorly sorted angular grains in a compact, clay-fine matrix

Greywacke or graywacke is a variety of sandstone generally characterized by its hardness, dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or lithic fragments set in a compact, clay-fine matrix. It is a texturally immature sedimentary rock generally found in Paleozoic strata. The larger grains can be sand- to gravel-sized, and matrix materials generally constitute more than 15% of the rock by volume. The term "greywacke" can be confusing, since it can refer to either the immature aspect of the rock or its fine-grained (clay) component.

<span class="mw-page-title-main">Hornfels</span>

Hornfels is the group name for a set of contact metamorphic rocks that have been baked and hardened by the heat of intrusive igneous masses and have been rendered massive, hard, splintery, and in some cases exceedingly tough and durable. These properties are due to fine grained non-aligned crystals with platy or prismatic habits, characteristic of metamorphism at high temperature but without accompanying deformation. The term is derived from the German word Hornfels, meaning "hornstone", because of its exceptional toughness and texture both reminiscent of animal horns. These rocks were referred to by miners in northern England as whetstones.

<span class="mw-page-title-main">Arkose</span> Type of sandstone containing at least 25% feldspar

Arkose or arkosic sandstone is a detrital sedimentary rock, specifically a type of sandstone containing at least 25% feldspar. Arkosic sand is sand that is similarly rich in feldspar, and thus the potential precursor of arkose.

<span class="mw-page-title-main">Quartz arenite</span>

A quartz arenite or quartzarenite is a sandstone composed of greater than 90% detrital quartz. Quartz arenites are the most mature sedimentary rocks possible, and are often referred to as ultra- or super-mature, and are usually cemented by silica. They often exhibit both textural and compositional maturity. The two primary sedimentary depositional environments that produce quartz arenites are beaches/upper shoreface and aeolian processes.

Rock microstructure includes the texture and small-scale structures of a rock. The words texture and microstructure are interchangeable, with the latter preferred in modern geological literature. However, texture is still acceptable because it is a useful means of identifying the origin of rocks, how they formed, and their appearance.

The Folk classification, in geology, is a technical descriptive classification of sedimentary rocks devised by Robert L. Folk, an influential sedimentary petrologist and Professor Emeritus at the University of Texas.

<span class="mw-page-title-main">Clastic rock</span> Sedimentary rocks made of mineral or rock fragments

Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus, chunks and smaller grains of rock broken off other rocks by physical weathering. Geologists use the term clastic with reference to sedimentary rocks as well as to particles in sediment transport whether in suspension or as bed load, and in sediment deposits.

This glossary of geology is a list of definitions of terms and concepts relevant to geology, its sub-disciplines, and related fields. For other terms related to the Earth sciences, see Glossary of geography terms.

<span class="mw-page-title-main">Gazzi-Dickinson method</span> Point-counting technique used in geology

The Gazzi-Dickinson method is a point-counting technique used in geology to statistically measure the components of a sedimentary rock, chiefly sandstone. The main focus part of the technique is counting all sand-sized components as separate grains, regardless of what they are connected to. Gazzi-Dickinson point counting is used in the creation of ternary diagrams, such as QFL diagrams.

<span class="mw-page-title-main">Lithic sandstone</span>

Lithic sandstones, or lithic arenites, or litharenites, are sandstones with a significant (>5%) component of lithic fragments, though quartz and feldspar are usually present as well, along with some clayey matrix. Lithic sandstones can have a speckled or gray color, and are usually associated with one specific type of lithic fragment.

Igneous rocks are found in Bukit Timah, Woodlands, and Pulau Ubin island. Granite makes up the bulk of the igneous rock. Gabbro is also found in the area and is found in an area called Little Guilin, named for its resemblance to Guilin in South China. This area is in Bukit Gombak. Sedimentary rocks are found on the western part of Singapore, which is mainly made of sandstone and mudstones. It also includes the southwestern area. Metamorphic rocks are found in the northeastern part of Singapore, and also on Pulau Tekong, off the east coast of Singapore. The rocks are mainly made up of quartzite, and also make up the Sajahat Formation.

<span class="mw-page-title-main">Iron-rich sedimentary rocks</span> Sedimentary rocks containing 15 wt.% or more iron

Iron-rich sedimentary rocks are sedimentary rocks which contain 15 wt.% or more iron. However, most sedimentary rocks contain iron in varying degrees. The majority of these rocks were deposited during specific geologic time periods: The Precambrian, the early Paleozoic, and the middle to late Mesozoic. Overall, they make up a very small portion of the total sedimentary record.