Quartz Quartz is hexagonal and commonly occurs as crystals ranging in size form microscopic to crystals weighing several tons. Where it crystallizes unhindered by other crystals, such as in cavities in rock or in a liquid containing few other crystals, it shows well-developed hexagonal prisms and sometimes showing apparent hexagonal pyramids or dipyramid. When it crystallizes in an environment where growth is inhibited by the surroundings, it rarely show crystal faces. It is also found as microcrystalline masses, such as in the rock chert, and as fibrous masses, such as in chalcedony. Vitreous lusture. As visible crystals, Quartz is one of the more common rock forming minerals. It occurs in siliceous igneous rocks such as volcanic rhyolite and plutonic granitic rocks. It is common in metamorphic rocks at all grades of metamorphism, and is the chief constituent of sand. Because it is highly resistant to chemical weathering, it is found in a wide variety of sedimentary r
COAL ORIGIN AND ITS TYPES FIGURE 1.1 ( COAL ) Stratified, compact, mass of plant debris modified chemically and physically by natural agencies, Plant debris mainly but not exclusively from terrestrial plants Natural agencies causing physical and chemical changes: bacteria & fungi, oxidation, reduction, hydrolysis, condensation; effect of heat and pressure in presence of water Physical changes: reduction in strength of woody cell structure, development of colloidal properties, increase in depth and brightness of color, increase in hardness and brittleness Chemical properties of a coal depends upon properties of the different constituents of the vegetable matter, the nature and extent of the changes Inorganic matter proportion in coal is small, oil shales and carbonaceous shales which differ from coal only in having inorganic matter as their major component, are not classed as coal Cannel coals