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
HYDROTHERMAL ORE DEPOSITS Figure 1.1 HYDROTHERMAL PROCESS Concentration by hot aqueous (water-rich) fluids flowing through fractures and pore spaces in rocks. The fluid temperature ranges from 50 to 500 degree C. These fluid can be the final product of volcanic differentiation or the ground water got heated by contact of magma or chamber. Hydrothermal deposits are produced when groundwater circulates to depth and heats up either by coming near to the hot igneous body at depth or by circulating to great depth along the geothermal gradient. Such hot water can dissolve valuable substances throughout a large volume of rock. As the hot water moves into cooler areas of the crust, the dissolved substances are precipitated from the hot water solution. If the cooling takes place rapidly, T hey might occur in open fractures or upon reaching a body of cool surface water, then precipitation will take place over a limi