Feldspar hardness

Miscellaneous Natural Abrasives. Powdered feldspar [68476-25-5] is used as a mild abrasive in cleansing powders, and clays are sometimes used in polishing powders. StauroHte [12182-56-8] is a complex hydrated aluminosiHcate of kon, of high density (3.74—3.83 g/mL) and a hardness of 7 to 8 on Mohs scale. It is primarily used as a sandblasting grit, but siHcosis hazards had cut production in 1987 about 25% compared to that... 

The hard rock deposits are mined mainly for feldspar with mica and quartz being accessory minerals. These deposits are extensive, often covering hundreds of square meters and are recognized by the light-colored, granite-like appearance with shiny mica flakes being a prominent feature. The mica content of these deposits ranges from approximately 6—10 wt %. 

Flake Mica. Flake mica is mined from weathered and hard rock pegmatites, granodiorite, and schist and gneiss by conventional open-pit methods. In soft, residual material, dozers, shovels, scrapers, and front-end loaders are used to mine the ore. Often kaolin, quartz, and feldspar are recovered along with the mica (see also Clays Silicon compounds). 

Hard rock mining of these ore bodies requkes drilling and blasting with ammonium nitrate and dynamite. After blasting, the ore is reduced in size with a drop ball and then loaded on tmcks for transportation to the processing plant. Mica, quartz, and feldspar concentrates are separated, recovered, and sold from the hard rock ore. 

Cementite, the term for iron carbide in steel, is the form in which carbon appears in steels. It has the formula Fe C, and thus consists of 6.67 wt % carbon and the balance iron. Cementite is very hard and britde. As the hardest constituent of plain carbon steel, it scratches glass and feldspar, but not quart2. It exhibits about two-thirds the induction of pure iron in a strong magnetic field, but has a much lower Curie temperature. 

The hardness of a mineral as measured by the Mohs scale is a criterion of its resistance to crushing [Fahrenwald, Trans. Am. In.st. Min. Metall. Pet. Eng., 112, 88 (1934)]. It is a fairly good indication of the abrasive character of the mineral, a factor that determines the wear on the grinding media. Arranged in increasing order or hardness, the Mohs scale is as fohows 1, talc 2, gypsum 3, calcite 4, fluoride 5, apatite 6, feldspar 7, quartz 8, topaz 9, corundum and 10, diamond. 

Intermediate Hardness (4) Fluorite, soft phosphate, magnesite, limestone (5) apatite, hard phosphate, hard limestone, chromite, bauxite (6) feldspar, ilmenite, orthoclase, hornblendes. 

Silica and Feldspar These are ground in silex-lined mills with flint balls (see Table 20-28). At a mine near Cairo, Illinois, silica is successfully crushed prior to ball-milling in American rotaiy impact mills having loose crushing rings made of hard alloy steel. The rings are easily replaced as they wear. 

Average (hardness 5.5-7 on Mohs scale) Basalt Feldspar... 

Geologists have found that the mineral quartzite as well as synthetic quartz is softened by water (Griggs and Blacic, 1965). Dry quartz crystals retain then-hardnesses to nearly 1000 °C, but are weakened considerably (nearly an order of magnitude) by the presence of water. Similar weakening is observed for olivine (Mg,Fe)2(Si04) and feldspar (KAlSi3Os). 

A large hard rock rutile deposit was discovered in central Chile. This ore is relatively complex with variable head grade of rutile ranging from 2% to 4% Ti02. The liberation of rutile occurs at about 100 mesh nominal size. The major gangue minerals present in this ore include feldspars, calcite and some silicates. 

Abrasives (DW, HC) Provide smoothing, scrubbing, or polishing action Hardness Calcite Feldspar Quartz Sand 0-55% 60-90% 0-15%... 

Quartz is an important network silicate (Section 12.10). A number of additional tetrahedral silicate-like materials possess some AIO4 tetrahedra substituted for the Si04 tetrahedra. Such structures offer a little larger hole in comparison to the entirely Si04 structures allowing alkali and alkaline-earth cations to be introduced. Feldspar (orthoclase) is one such mineral. The alumino-silicate networks are almost as hard as quartz. For feldspar and other tetrahedral networks the number of oxygen atoms is twice the summation of silicon and other MO4 cations. 

As one might expect there is an approximate correlation between the solid state structure and the physical properties of a particular silicate. For instance, cement contains discrete 8104 units and is soft and crumbly asbestos minerals contain double chains of 8104 units and are characteristically fibrous mica contains infinite layers of 8104 units, the weak bonding between the layers is easily broken, and micas show cleavage parallel to the layers and granite contains feldspars that are based on three-dimensional 8104 frameworks and are very hard. 

The distinctly differentiated results obtained, for example, for different faces of quartz or feldspar crystal, with clear observed differences depending on structure and compactness of the material under test, are an argument for wide use of the Mackensen blower in the study of engineering properties of rocks and ceramic materials and also in hardness estimation of minerals. 

HALLEFI.INTA. A Swedish term for hard, dense, mciamorphic rocks composed chielly of microscopic crystals of quartz and feldspar with occasional phenocry.sls. Accessory minerals may he hornblende, chlorite, hematite nr magnetite. The Icxlurc and composition of hAllcfiinta suggests ihai ii is die metamorphosed equivalent of acid lava Hows or luffs. 

Flake mica is also produced as a by-produel from processing feldspar ore (hard granodinrilc) from mica schist which normally contains front 30-60 lecrvstallized muscovite mica along with quartz and iron minerals. The quartz is usually not suitable lor glass sand or high purity material, however. 

There is an extensive literature on the gross structure and microstructure of feldspars and the methods for determining them. Three of the most recent comprehensive treatments at review level are found in references (14) and (15) and in the classic, "Feldspar Minerals", by J.V. Smith (16), now in its second edition. Optical methods, X-ray diffraction and electron diffraction are all so well-established that it hardly seems necessary to do more than give a brief reminder of their particular characteristics. 

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