Coal is a solid combustible organic rock.Coal petrology is a science that regards coal as an organic rock and studies the material composition, structure, nature, origin and rational utilization of coal mainly by physical methods.There are the following classification methods:
1. The vitrinite
The vitreous coal color is dark, the luster is strong, is in the coal color deepest and the luster strongest composition.
Features of vitrinite:
(1) the texture is pure, uniform structure, with shell-like fracture and endogenous fissure.(2) mirror coal brittle, easily broken into angular shape small pieces.(3) in the coal seam, mirror coal is often convex lenticular or strip, strip thickness of several millimeters to 1~2cm, sometimes linear texture in the presence of bright coal and dark coal.
The microscopic composition of vitrinite is single, which is mainly formed by gelation of the woody microscopic structure of plants.
Properties: high V, H, strong adhesion, less mineral content
Appearance like charcoal, gray black color, with a clear fibrous structure and silk luster, silk charcoal loose porous, brittle, can touch.The cellular space of silk carbon is sometimes filled with minerals, which is called mineralized silk carbon.
In the coal seam, the amount of silk carbon is generally not large, and it is often a flat lens. When observed under the microscope, the microscopic composition of silk carbon is also single, and it is a simple coal and rock composition. It is mainly caused by the slow oxidation of plant woody fiber tissue in the water-deficient and oxygen-rich environment or the formation of forest fire.
(1) in the coal seam, the carbon filament is usually a flat lens body along the stratification plane of the coal seam, the thickness is more than 1~2mm to a few millimeters, sometimes can form a discontinuous thin layer;In some areas, the thickness of the carbon layer can be tens of centimeters or more.
(2) the porosity of carbon filament, oxygen absorption is strong, more coal seam prone to spontaneous combustion.
Properties: dense and hard, high specific ratio, low H, high C, low V, no adhesion, poor selectivity, large porosity.
3. Light coal
Bright coal is second only to vitreous coal in luster. It is usually black.It is formed by the gelation of the lignocellulosic tissue of plants under the reduction condition of overlying water, and mixed with some other components and mineral impurities brought by water or wind.
(1) brittle, relatively flat section, (2) the specific gravity is smaller.(3) the degree of uniformity of bright coal is not as good as mirror coal, the surface is faintly visible fine bedding.(4) bright coal sometimes there are endogenous cracks, but not as well as the development of mirror coal.Often show thicker stratification, sometimes even constitute the whole coal seam.
In the coal seam, bright coal is the most common macroscopic coal rock composition.
The quality of bright coal is similar to vitrinite, but the quality is worse than vitrinite.
4. The dark coal
The sheen of dark coal is dim and generally grayish black.The composition of dark coal is more complicated.It is under the condition of oxygen in living water, enriched crustacetic group, inert group or mixed more minerals into the transformation.Dark coal containing inert or mineral substances.
(1) dense hard, major, toughness, not broken, relatively rough section, (2) generally do not develop endogenous crack.(3) in the coal seam, dark coal is a common macroscopic coal rock composition, often thick, thin different stratification, can also constitute the whole coal seam.
Properties: it depends on the content of each component, such as rich in stable components, high V, H, strong adhesion;Rich in silk carbonization components, high mineral content, high density, low V, weak adhesion.