Minerals orthoclase

Among the most common minerals are the feldspars and clays. These materials have been used for centuries in the manufacture of pottery, china, brick, cement, and other materials. Feldspars include the mineral orthoclase, K20 A1203 6Si02, but this formula can also be written as K2Al2Si60i6- Under the influence of carbon dioxide and water, this mineral weathers by a reaction that can be shown as... 

K2SO-2 MgSO, and halite and (5) kainite ore, kainite [1318-72-5] 4(KC1 MgSO -11H20, and halite. More than 90% of the estimated potassium reserves occur principally as sylvinite and camaUitite (107). Sylvite, the richest of the minerals at 63% K2O, is the principal economically exploitable reserve. In addition, there are four principal insoluble potassium sUicate minerals, glauconite, leucite, nepheline, and orthoclase—sanidine which range in K2O content from 7 to 22%. These minerals are plentihil but for economic reasons may never be exploited for potassium. 

The hardness of an enamel surface is an important property for such items as enamelled sink units, domestic appliances, washing machine tubs which have to withstand the abrasive action of buttons, etc. On Moh s scale most enamels have a hardness of up to 6 (orthoclase). There are two types of hardness of importance to users of enamel, viz. surface and subsurface. The former is more important for domestic uses when one considers the scratching action of cutlery, pans, etc. whereas subsurface hardness is the prime factor in prolonging the life of enamelled scoops, buckets, etc. in such applications as elevators or conveyors of coal and other minerals. 

Figure 8.22 Closure temperature Tc as a function of the rate of loss for a spherical geometry [equation (8.7.6)]. The numbers on the curves are for different fractions lost by the mineral. Amphibole data from Harrison (1981), orthoclase data from Foland (1974). Points A, A, B, B see text.

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. 

Figure 7.12. Examples of epitaxy observed in minerals, (a) lyrite on marcasite (b) quartz on calcite (c) albite on orthoclase.

In the intermediate layer a surplus of negative charge arises. This is compensated by cations of the O layer [2,3,4], initially Mg2+ and Fe2+. The thus formed vacancy in the O layer is filled with a Si4+ from the T layer [4] or an Al3+ from the O layer. By now the disintegration has reached an advanced stage. An example of erosion in a chemical equation is the formation of the clay mineral kaolinite from orthoclase, an alkaline feldspar. 

Heavy minerals and accessory minerals Zircon, rutile, tourmaline, orthoclase, biotite — Chlorides, sulfates, nitrates —... 

Trivalent iron is an effective activator when it is free of the effects of ferrous iron. Because of the larger value of Dq, the emission is shifted to 700 - 750 nm in the deep red when Fe + is present on tetrahedral sites. Fe + in octahedral coordination is predicted to emit in the near infrared at about 900 to 1000 nm but is rarely observed and is thus indicated by a dashed line in Figure 5. Fe luminescence in minerals is mainly observed when Fe + substitutes for Al3+ in tetrahedral sites in aluminosilicates. Observations on feldspars (15) provide the transition sketched on Figure 5. In the orthoclase structure the Stokes shift is 1500 wavenumbers. Trivalent iron is the most likely activator for luminescence seen in many terrestrial feldspars and feldspar-containing rocks. The characteristic 700-750 nm band is weak or absent in lunar feldspars (16,17). 

The feldspar minerals are aluminosilicates of alkali and alkali-earth cations and are chemically classified by the mole percentages of three end-members orthoclase (Or KAlSi308) albite (Ab NaAlSi308) anorthite (An CaAl2Si208). The three constitute a ternary system with extensive solid solutions along the Or-Ab and Ab-An axes. The nomenclature on the basis of the mole percentages... 

Faye, G. H. (1969) The optical absorption spectrum of tetrahedrally coordinated Fe3+ in orthoclase. Canad. Mineral., 10,112-17. 

Some of the most common igneous minerals are quartz, potassium feldspars (orthoclase and microcline), plagioclase feldspars (albite, anorthite), micas (muscovite, biotite), olivine, and members of the amphibole and pyroxene groups. Many other minerals are found in igneous rocks, most of which occur in only very small amounts. These are called accessory minerals, the most common of these are corundum, pyrite, magnetite, zircon, rutile, apatite, and members of the garnet group. 

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