ORIGIN OF COAL

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COAL GEOLOGY PRESENTED BY : AVISHEK MUKHERJEE DEPT. OF GEOLOGICAL SCIENCES JADAVPUR UNIVERSITY KOLKATA 32

WHAT IS COAL? : 

WHAT IS COAL? Coal is an organoclastic sedimentary rock, composed essentially of lithiified plant debris. “COAL” : Derived from SANSKRIT root “KALA” means “black”. Coal is known in different terms in different countries. Sweden: KOL German: KOHLE Anglo-Saxon :COLE Hindi : KOELA ORIGIN OF COAL IS VEGETATIVE. COAL NOT A MINERAL, RATHER CONSIDERED AS ROCK.

TYPES OF COAL : 

TYPES OF COAL COAL Sapropelic coal Humic coal Anthracite Bituminous Lignite (brown coal) Peat Cannel coal Boghead coal Another two types of coal: Paper coal Coloured coal

DIFFERENT TYPES OF COAL : 

DIFFERENT TYPES OF COAL Peat considered to be a precursor of coal, has industrial importance as a fuel in some regions, for example, Ireland and Finland. In its dehydrated form, peat is a highly effective absorbent for fuel and oil spills on land and water Lignite, also referred to as brown coal, is the lowest rank of coal and used almost exclusively as fuel for electric power generation. Jet is a compact form of lignite that is sometimes polished and has been used as an ornamental stone since the Iron Age. Sub-bituminous coal whose properties range from those of lignite to those of bituminous coal are used primarily as fuel for steam-electric power generation. Additionally, it is an important source of light aromatic hydrocarbons for the chemical synthesis industry. Bituminous coal, dense mineral, black but sometimes dark brown, often with well-defined bands of bright and dull material, used primarily as fuel in steam-electric power generation, with substantial quantities also used for heat and power applications in manufacturing and to make coke. Anthracite, the highest rank; a harder, glossy, black coal used primarily for residential and commercial space heating. It may be divided further into metamorphically altered bituminous coal and petrified oil, as from the deposits in Pennsylvania.

CAKING AND COKING COALS : 

CAKING AND COKING COALS CAKING COAL-Coal that softens and agglomerates on heating and after volatile matter has been driven off at high temperatures; produces a hard gray cellular mass of coke. COKING COAL-The caking coals used in the industry for different purposes, called coking coals. Coal that can be converted into useful coke that must be strong enough to withstand handling. There is no direct relation between the elementary composition of coal and coking quality, but generally coals with 80% to 90% carbon on a dry, ash-free basis are most satisfactory. All caking coals are not good coking coals, but all coking coals are caking coals.

MACERALS : 

MACERALS A maceral is a component 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. It is mainly plant materials. It is different types- internites,vitrinites and liptinites. Inertinite is considered to be the equivalent of charcoal and degraded plant material. Vitriniteis 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. Liptinite 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.

NATURE OF MACERALS : 

NATURE OF MACERALS 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 whether the coal is lignite, brown coal, bituminous coal, anthracite or graphite. 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.

VITRINITE : 

VITRINITE 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 etc. The vitrinite group, which consists of various individual Vitrinite macerals is the most common component of coals. It is also abundant in kerogens that are derived from the same biogenic precursors as coals, namely land plants and humic peats. Vitrinite forms diagenetically by the thermal alteration of lignin and cellulose in plant cell walls. It is therefore common in sedimentary rocks that are rich in organic matter, such as shales and marls with a terrigenous origin, or some terrigenous content. Conversely, carbonates, evaporites and well-sorted sandstones have very low vitrinite contents. Vitrinite is absent in pre-Silurian rocks because land plants had not yet evolved

MODE OF OCCURRENCE : 

MODE OF OCCURRENCE Coal seams interbeded with sandstone, shale, siltstone etc sedimentary units.

STRATIGRAPHIC POSITION : 

STRATIGRAPHIC POSITION Principal store house Of coal in India.

ORIGIN OF COAL : 

ORIGIN OF COAL Accumulation of vegetal matters occurs for a long time span and also buried for a considerable time span. Two theories for accumulation of coal  Growth in-situ theory. Drift theory.

GROWTH IN-SITU THEORY : 

GROWTH IN-SITU THEORY This theory states the coal was fossilized on the site of growth due to Tectonism or some other reasons. Supporting evidences of this theory are A vast amount of plant materials accumulated in-situ in the present day swamps. Many fossilized tree-trunks found in erect positions with their roots fixed in the under clays that lie beneath the coal seams. A comparatively pure state of coal seams indicates that the materials accumulated without getting mixed with the adventitious materials and not transported along the sediments.

DRIFT THEORY : 

DRIFT THEORY This theory states the coal seams have been formed as a result of drifting and subsequent accumulation of plant bodies away from the place of growth. This coals are depleted in Na, K etc. Supporting evidences of this theory are No under clays, representing the soil at the root are associated with the coal. Stems with roots in upright positions are not found. Beds of coals are observed to branch out, which only characteristics of drifted matters. Coal seams associated with sedimentary rocks and itself behave like a stratified sedimentary rocks. Presence of channel sands indicating criss-cross movement of water through swamps.

FORMATION OF COAL : 

FORMATION OF COAL

BASIC REQUIREMENTS FOR COAL FORMATION : 

BASIC REQUIREMENTS FOR COAL FORMATION Humid conditions. Substantial growth of vegetation with at least some woody or fibrous parts. Rapid burial. Calm and quiet environment. Sufficient amount of standing water.

TRANSFORMATION OF VEGETABLE MATTERS : 

TRANSFORMATION OF VEGETABLE MATTERS Transformation occurs in two distinct stages. 1. BIOCHEMICAL STAGES . 2. COALIFICATION STAGES. BIOCHEMICAL STAGE Activities of aerobic bacteria. Activities of anaerobic bacteria. Hydrogen ion concentration. Redox potential.

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COALIFICATION STAGE Progressive change in composition of organic matters in the transformation of coal. FIRST PHASE: Decarboxylation and dehydroxylation. Evolution of low rank coal-lignites.% of oxygen decreases. H/C0.83 SECOND PHASE: Dehydrogenation process. Decrease in H content. Evolution of high rank coal-bituminous. H/C0.56. THIRD PHASE: Demethylization process dominant. Evolution of semi anthracite and anthracite.

CONCLUSIONS : 

CONCLUSIONS From all the information following conclusions can be drawn for the formation of coal: Appreciable enough amount of plant materials. Surficial contact should be cutoff. Concentration of hydrogen ion and Redox potential. Coalification process occurs in three phases. Time. Dehydroxilation,decarboxylation, dehydration, demethylization and aromatization are important processes for changes to low rank to high rank coal. Gradual decrease in oxygen content and increase in carbon/hydrogen ratio. More and more aromatization.

Thank you…………….. : 

Thank you……………..