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A maceral is a component, organic in origin, of coal or oil shale. The term 'maceral' in reference to coal is analogous to the use of the term 'mineral' in reference to igneous or metamorphic rocks. Examples of macerals are inertinite, vitrinite, and liptinite.
Inertinite is considered to be the equivalent of charcoal and degraded plant material. It is highly oxidised in nature and may be said to be burnt. A large portion of South Africa's coal reserves consist of inertinite.
Vitrinite is shiny, glass-like material that is considered to be composed of cellular plant material such as roots, bark, plant stems and tree trunks. Vitrinite macerals when observed under the microscope show a boxlike, cellular structure, often with oblong voids and cavities which are likely the remains of plant stems. This has a high calorific value (24 - 28 MJ/kg) and a large proportion of volatile matter (24 - 30%). It often occurs interbanded or interlaminated with inertinite and can be recognised as bright bands.
Liptinite macerals are considered to be produced from decayed leaf matter, spores, pollen and algal matter. Resins and plant waxes can also be part of liptinite macerals. Liptinite macerals tend to retain their original plant form, i.e., they resemble plant fossils. These are hydrogen rich and have the highest calorific values of all coal macerals.
Macerals of liptinite are sporinite, cutinite, resinite, alginite (telalginite and lamalginite), liptodetrinite, fluorinite, and bituminite.
Macerals are considered to be dehydrogenated plant fragments. Evidence for this includes remnant pollen spores, fossilised leaves, remnant cellular structure and similar. In rare cases, maceral and fossilised pollen can be found in terrestrial sedimentary rocks.
Maceral maturity can be estimated by vitrinite reflectance. This gives information on the carbon, hydrogen and nitrogen composition of the coal, and determines the type of coal: lignite, bituminous coal, or anthracite.
Macerals found in kerogen source rocks are often observed under the microscope to determine the kerogen maturity of the sedimentary formations. This is a vital component of oil and gas exploration.
Macerals are observed under the petrographic microscope under reflected light. Coal fragments must be extremely highly polished down to less than half a micrometre before they can be observed under the microscope.
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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.
Bituminous coal, or black coal, is a type of coal containing a tar-like substance called bitumen or asphalt. Its coloration can be black or sometimes dark brown; often there are well-defined bands of bright and dull material within the seams. It is typically hard but friable. Its quality is ranked higher than lignite and sub-bituminous coal, but lesser than anthracite. It is the most abundant rank of coal, with deposits found around the world, often in rocks of Carboniferous age. Bituminous coal is formed from sub-bituminous coal that is buried deeply enough to be heated to 85 °C (185 °F) or higher.
Kerogen is solid, insoluble organic matter in sedimentary rocks. It consists of a variety of organic materials, including dead plants, algae, and other microorganisms, that have been compressed and heated by geological processes. All the kerogen on earth is estimated to contain 1016 tons of carbon. This makes it the most abundant source of organic compounds on earth, exceeding the total organic content of living matter 10,000-fold.
Vitrinite is one of the primary components of coals and most sedimentary kerogens. Vitrinite is a type of maceral, where "macerals" are organic components of coal analogous to the "minerals" of rocks. Vitrinite has a shiny appearance resembling glass (vitreous). It is derived from the cell-wall material or woody tissue of the plants from which coal was formed. Chemically, it is composed of polymers, cellulose and lignin.
Palynology is the study of microorganisms and microscopic fragments of mega-organisms that are composed of acid-resistant organic material and occur in sediments, sedimentary rocks, and even some metasedimentary rocks. Palynomorphs are the microscopic, acid-resistant organic remains and debris produced by a wide variety plants, animals, and Protista that have existed since the late Proterozoic.
Inertinite refers to a group of partially oxidized organic materials or fossilized charcoals, all sharing the characteristic that they typically are inert when heated in the absence of oxygen. Inertinite is a common maceral in most types of coal. The main inertinite submacerals are fusinite, semifusinite, micrinite, macrinite and funginite, with semifusinite being the most common. From the perspective of coal combustion, inertinite can be burned to yield heat, but does not yield significant volatile fractions during coking.
In coal geology, liptinite is the finely-ground and macerated remains found in coal deposits. It replaced the term exinite as one of the four categories of kerogen. Liptinites were originally formed by spores, pollen, dinoflagellate cysts, leaf cuticles, and plant resins and waxes.
A microfossil is a fossil that is generally between 0.001 mm and 1 mm in size, the visual study of which requires the use of light or electron microscopy. A fossil which can be studied with the naked eye or low-powered magnification, such as a hand lens, is referred to as a macrofossil.
Relative dating is the science of determining the relative order of past events, without necessarily determining their absolute age. In geology, rock or superficial deposits, fossils and lithologies can be used to correlate one stratigraphic column with another. Prior to the discovery of radiometric dating in the early 20th century, which provided a means of absolute dating, archaeologists and geologists used relative dating to determine ages of materials. Though relative dating can only determine the sequential order in which a series of events occurred, not when they occurred, it remains a useful technique. Relative dating by biostratigraphy is the preferred method in paleontology and is, in some respects, more accurate. The Law of Superposition, which states that older layers will be deeper in a site than more recent layers, was the summary outcome of 'relative dating' as observed in geology from the 17th century to the early 20th century.
Cannel coal or candle coal is a type of bituminous coal, also classified as terrestrial type oil shale. Due to its physical morphology and low mineral content cannel coal is considered to be coal but by its texture and composition of the organic matter it is considered to be oil shale. Although historically the term cannel coal has been used interchangeably with boghead coal, a more recent classification system restricts cannel coal to terrestrial origin, and boghead coal to lacustrine environments.
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.
In geology, texture or rock microstructure refers to the relationship between the materials of which a rock is composed. The broadest textural classes are crystalline, fragmental, aphanitic, and glassy. The geometric aspects and relations amongst the component particles or crystals are referred to as the crystallographic texture or preferred orientation. Textures can be quantified in many ways. The most common parameter is the crystal size distribution. This creates the physical appearance or character of a rock, such as grain size, shape, arrangement, and other properties, at both the visible and microscopic scale.
Torbanite, also known historically as boghead coal or kerosene shale, is a variety of fine-grained black oil shale. It usually occurs as lenticular masses, often associated with deposits of Permian coals. Torbanite is classified as lacustrine type oil shale. A similar mineral, cannel coal, is classified as being a terrestrial form of oil shale, not a lacustrine type.
Oil shale geology is a branch of geologic sciences which studies the formation and composition of oil shales–fine-grained sedimentary rocks containing significant amounts of kerogen, and belonging to the group of sapropel fuels. Oil shale formation takes place in a number of depositional settings and has considerable compositional variation. Oil shales can be classified by their composition or by their depositional environment. Much of the organic matter in oil shales is of algal origin, but may also include remains of vascular land plants. Three major type of organic matter (macerals) in oil shale are telalginite, lamalginite, and bituminite. Some oil shale deposits also contain metals which include vanadium, zinc, copper, and uranium.
In petroleum geology, source rock is rock which has generated hydrocarbons or which could generate hydrocarbons. Source rocks are one of the necessary elements of a working petroleum system. They are organic-rich sediments that may have been deposited in a variety of environments including deep water marine, lacustrine and deltaic. Oil shale can be regarded as an organic-rich but immature source rock from which little or no oil has been generated and expelled. Subsurface source rock mapping methodologies make it possible to identify likely zones of petroleum occurrence in sedimentary basins as well as shale gas plays.
Marker horizons are stratigraphic units of the same age and of such distinctive composition and appearance, that, despite their presence in separate geographic locations, there is no doubt about their being of equivalent age (isochronous) and of common origin. Such clear markers facilitate the correlation of strata, and used in conjunction with fossil floral and faunal assemblages and paleomagnetism, permit the mapping of land masses and bodies of water throughout the history of the earth. They usually consist of a relatively thin layer of sedimentary rock that is readily recognized on the basis of either its distinct physical characteristics or fossil content and can be mapped over a very large geographic area. As a result, a key bed is useful for correlating sequences of sedimentary rocks over a large area. Typically, key beds were created as the result of either instantaneous events or very short episodes of the widespread deposition of a specific types of sediment. As the result, key beds often can be used for both mapping and correlating sedimentary rocks and dating them. Volcanic ash beds and impact spherule beds, and specific megaturbidites are types of key beds created by instantaneous events. The widespread accumulation of distinctive sediments over a geologically short period of time have created key beds in the form of peat beds, coal beds, shell beds, marine bands, black shales in cyclothems, and oil shales. A well-known example of a key bed is the global layer of iridium-rich impact ejecta that marks the Cretaceous–Paleogene boundary.
Cutinite is a liptinite maceral formed from terrestrial plant cuticles, and often found in coal deposits. It is classified as a Type II kerogen.
Pyrobitumen is a type of solid, amorphous organic matter. Pyrobitumen is mostly insoluble in carbon disulfide and other organic solvents as a result of molecular cross-linking, which renders previously soluble organic matter insoluble. Not all solid bitumens are pyrobitumens, in that some solid bitumens are soluble in common organic solvents, including CS
2, dichloromethane, and benzene-methanol mixtures.
Bituminite is an autochthonous maceral that is a part of the liptinite group in lignite, that occurs in petroleum source rocks originating from organic matter such as algae which has undergone alteration or degradation from natural processes such as burial. It occurs as fine-grained groundmass, laminae or elongated structures that appear as veinlets within horizontal sections of lignite and bituminous coals, and also occurs in sedimentary rocks. Its occurrence in sedimentary rocks is typically found surrounding alginite, and parallel along bedding planes. Bituminite is not considered to be bitumen because its properties are different from most bitumens. It is described to have no definite shape or form when present in bedding and can be identified using different kinds of visible and fluorescent lights. There are three types of bituminite: type I, type II and type III, of which type I is the most common. The presence of bituminite in oil shales, other oil source rocks and some coals plays an important factor when determining potential petroleum-source rocks.
Funginite is a maceral, a component, organic in origin, of coal or oil shale, exhibiting several different physical properties and characteristics under particular conditions; its dimensions are based upon its source and place of discovery. Furthermore, it is primarily part of a group of macerals that naturally occur in rocks containing mostly carbon constituents, specifically coal. Due to its nature, research into the chemical structure and formula of funginite is considered limited and lacking. According to Chen et al. referencing ICCP, 2001, alongside the maceral secretinite, they "are both macerals of the inertinite group, which is more commonly known as fossilized charcoal, and were previously jointly classified as the maceral sclerotinite". In the scientific community, the discernment between the two does not remain entirely clear, but there are slight particular and specific differences in regards to the composition between both. It is also the product of fungal development on these carbon rich sedimentary rocks.