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Minerals P-T
Quartz
Name
Quartz
Chemistry
SiO2
Uses
Quartz is used as a component of glass, ceramics, refractories, cements, and mortar; as an abrasive; as a chemical raw material for the manufacture of sodium silicate, silicon carbide, silicon metals, organic silicates, and silicones; and as a component in numerous other industrial materials.
Color
Transparent, yellow, purple and all the colors
Hardness
7
Specific gravity
2.651
Quartz which is the most abundant silica mineral and which occurs in most igneous and practically all metamorphic and sedimentary rocks, is nearly pure silicon dioxide.
It has also been found in some lunar rocks and meteorites. The name quartz is believed to have originated in the early 1500s from the Saxon word querklufterz (cross-vein ore), which was corrupted to quererz and then to quartz. Quartz was well known to the ancients, who called it crystal or rock crystal.
The Brandberg quartz crystals from the Gobobos mountains are very interesting. In the Gobobos Mountains the geodes often carry what the local "stone community" refer to as window quartz. These hopper crystals were crystallization from a super-saturated solution progressed so rapidly that it concentrated along the edges of the crystal planes with virtually no deposits on the center of the developing crystal faces, resulting in a skeletal crystal. These can be described as looking like a set of windows one stacked upon the other hence the local nomenclature.
Occasionally a renewed charge of super saturate solution will renew the growth of the crystal, resulting in the airtight trapping of the fluid and gas within the crystal, which when cooled contracts, displaying a distinct moving gas bubble in the solid crystal.
The Gobobos crystals are noted for their
inclusions and
windowing (skeletal quartz) that they exhibit almost exclusively to this locality.
Very fine-grained and cryptocrystalline varieties of quartz are numerous. Collectively called chalcedy, these varieties form slowly from evaporating or cooling solutions as crusts and fillings of veins and open spaces.
When color banding is conspicuous, the variety is called agate.
Agate with numerous flat bands of white, black, or dark brown is called onyx.
Translucent red or brown chalcedonic quartz colored by iron oxides.
Green varieties colored by chlorite, amphiboles, or nickel minerals;
Mottled moss agates are used as semiprecious stones.
Bloodstone is a green variety of chalcedonic quartz with red spots. Chalcedonic quartz is often colored by chemical processes.
Finely crystallized quartz called chert and flint occurs within calcareous or silty sedimentary rock as gray or black layers or nodules.
Jasper is very fine-grained quartz with abundant incorporated iron oxides--it may be red, brown, yellow, dark gray, or black.
Amethyst may be transformed to citrine at 250¡ C (482¡ F) or higher. Vigorous rubbing of one quartz crystal by another may also produce visible light (triboluminescence).
Quartz can be dissolved in hot water or steam and is thus transported from place to place in the Earth, being deposited by cooling of the transporting fluid or by release of pressure. Because quartz is relatively resistant to mechanical abrasion, it is abundant in stream sediments, on beaches, and in wind-blown sands. Quartzite and sandstone are mostly quartz, and many other sedimentary and metamorphic rocks contain substantial proportions of quartz.Quartz is made of nearly pure silicon dioxide (SiOM) and is colorless and transparent when pure.
Quartz has no cleavage and fails by brittle fracture; the fracture surfaces have vitreous luster.Quartz occurs in a wide range of crystal sizes, from single crystals weighing many tons to cryptocrystalline varieties whose crystallinity may be seen only with the aid of an electron microscope.
Because the polar axes differ on each end, the application of mechanical stress to such an axis produces electrical charges of opposite sign at each end (piezoelectricity); conversely, applied electrical fields produce mechanical stresses. The piezoelectric property makes quartz valuable in pressure gauges, electronic frequency-control devices, radios, and other applications
