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
DARWAR SUPER GROUP THE ARCHAEN ROCK SYSTEM – DARWAR SUPER GROUP THEY ARE BEST DEVELOPED IN SITSES OF KARNATAKA AND THE ADJOINING STATES THE SEDIMENTARY OF THE DARWAR GROUP ARE DEPOSITED IN THE BASEMENT OF THE ”FUNDAMENTAL GNEISSES COMPLEX ” LITHOLOGY : · THE CHIEF ROCK TYPE IN THE DARWAR GROUP IS GNEISSES AND GRANITES · THEY COVER THE MAJOR PART OF SOUTH INDIA · MANY ELONGATED BELTS OF SCHISTOSE ROCKS ARE ENCLOSED WITHIN THESE ROCKS · THE SCHISTOSE ROCKS ARE FOLDED ISOCLINALLY AND EXHIBITED A STEEP DIP TOWARDS THE EAST CLASSIFICATION : · IGNEOUS INTRUSION = (FELCITE AND PHORPYRIC GROUP , CHARNOCHITE , CHAMPIAN GNEISS , PENINSULAR GNEISSCLOSEPET GRANITE ) · UPPER DARWAR = FERRUGINIOUS QUARTZITE , LIMESTONE , CONGLOMERATE , QUARTZITE , CALCARIOUS SILTS. · MIDDLE DARWAR =GRANITE ROCK WITH GNEISSOSSE STRUCTURE ,QUARTZITE , CONGLOMERATE , LIMESTONE , CHLORITE SCHIST ,SERISITE SCHIST , BAN