Feldspar

Feldspars are tectosilicates (multiplicity = 4, periodicity = 4, dimensionality = 3) the tetrahedral groups [TO4] share all their comers with neighboring [TO4] units, thus forming a rigid tridimensional network. In feldspars, 25 to 50% of the silicon atoms are replaced by AF. The basic stmcture of the network is made up of four-member rings of [TO4] groups, two-by-two in an upward- and downward- 

Feldspars are the most abundant minerals of igneous rocks, where their ubiquity and abundance of their components influence normative classifications. They are also abundant in gneisses, and may be observed in several facies of thermal and regional metamorphic regimes. Notwithstanding their alterability, they are ubiquitously present in sedimentary rocks, as authigenic and/or detritic phases. Only in carbonaceous sediments is their presence subordinate. 

B 100 ppm Forms pure component NaBSiOg (reedmergnerite) maximum observed amount in mixture corresponds roughly to 1 weight % B2O5 (Desborough, 1975). 

Ga 10-100 ppm Tendencially correlated to Na highest concentration observed in pegmatites. 

Ti 30-60 ppm Occasionally high concentrations (up to 600-700 ppm) in intermediate members of plagioclase series (labradorite bytownite). 

The pale yellow color in feldspar is due to Fe in tetrahedral Si/Al site. This color is often masked by the pervasive turbidity of common feldspars. Smoky color, the 

Steady-state luminescence of feldspars is well studied. The following impurity centers have been found TL, Pb , Pb , REE - (Ce, Dy, Sm, Tb, Nd), Eu - , Mn , Fe , Cr (Tarashchan 1978 Gorobets and Rogojine 2001 Gotse 2000 Waychunas 1989 Kuznetsov and Tarashchan 1988 Bakhtin and Moroshkin 1986 Krbetschek et al. 2002 White et al. 1986). 

Luminescence of monovalent Pb was firstly proposed for explanation of IR luminescence band peaking at 860 nm in emission spectrum of feldspars 

Excitation by CW laser with 780 run revealed several luminescence lines in albite (Fig. 4.101) which may be evidently ascribed to Fe , Nd and Yb , while microcline revealed mainly emission bands under excitation by 532 run peaking at 715, 720, 865 and 870 nm (Fig. 4.102.) The origin of those bands needs additional study including decay times and excitation spectra. 

Silica makes up 12.6 mass-% of the Earth crust as crystalline and amorphous forms. It was found that both modifications show similar main luminescence bands, 

The pale yellow color in feldspar is due to Fe in a tetrahedral Si/Al site. This color is often masked by the pervasive turbidity of common feldspars. A smoky color, the result of radiation damage from the decay of K-40, is also common but often masked. The blue color in the amazonite variety of potassium feldspar (and pale-blue albite) is from the interaction of trace amounts of Pb in the feldspar with ionizing radiation. Lead-containing feldspars with a higher 

The natural feldspars in our study consisted of twelve samples. Concentrations of rare-earth elements in one of them are presented in Table 4.16. The laser-induced time-resolved technique enables us to detect Pb, Gd +, Ce +, Eu +, Eu +, Tb +, Er +, Dy +, Sm +, Nd +, Mn +, Fe + and possibly Cr + emission (Figs. 4.43-4.45). 

Silica makes up 12.6 mass-% of the Earth s crust as crystalline and amorphous forms. It was found that both modifications show similar main luminescence bands, namely a blue one centered at 450 nm ascribed to which substitutes for Si, red centered at 650 nm linked with non-bridge O, and dark-red at 700-730 nm linked with Fe. Time-resolved luminescence of hydrous volcanic glasses with different colors and different Fe, Mn, and H2O contents were measured and interpreted (Zotov et al. 2002). The blue band with a short decay time of 40 ns was connected with T2( D)- Ai ( S) and Ai C G)- Ai ( S) ligand field transitions of Fe , the green band with a decay time of approximately 250 ps with a Ti( G)- Ai( S) transition in tetrahedrally coordinated Mn , while the red band with a much longer decay time of several ms with T1 (4G)- Ai( S) transitions in tetrahedrally coordinated Fe . We detected Fe in the time-resolved luminescence spectrum of black obsidian glass (Fig. 4.43d). 

The ionic radius of aluminum in octahedral coordination is of 0.67 A. The main substituting luminescence centers are Cr with an ionic radius of 0.75 A in octahedral coordination, Mn and Mn + with ionic radii of 0.81 and 0.67 A in octahedral coordination and and V with ionic radii of 0.93,0.78 

Four feldspathic minerals are likely to enter the composition of silicate ceramic 

Potassic feldspar is particularly appreciated by ceramists because its reaction with siUca leads to the formation of a liquid whose relatively high viscosity decreases slightly when the temperature increases. This behavior is considered as a guarantee against the excessive deformation of the pieces during the heat treatment. 

Natural feldspars used for the preparation of ceramics are mineral mixtures. Thus, the commercial potassium products can contain between 2.5 and 3.5% of albite mass, whereas anorthite and a small quantity of orthoclase, between 0.5 and 3.2%, are often present in the available sodium feldspars [MAN 94]. They can also be incorporated into the paste in the form of feldspathic sand. When these natural products are heated, mixed and homogenous feldspar is formed. This compoimd. 

Silica, Si02, is a polymorphic raw material found in nature in an amorphous (opal, pebbles) or crystallized form (quartz, cristobalite and tridymite). Sand contains between 95 and 100% of quartz mass. It is the most frequently used temper in the ceramic industry. To contribute significantly to the mechanical strength of the raw parts, it must consist of much coarser particles than those of clay. In the modem manufacturing processes of stonewares and porcelains, it is customary to use relatively fine sand grains (20 to 60 pm). 

When a ceramic is fined, the sand can react, particularly with the fluxes. This reaction is seldom complete. The transformation of residual quartz into cristobalite can then start from 1,200°C onwards. It is favored by the rise in temperature, the use of fine grained sand, the presence of certain impurities and a reducing atmosphere [JOU 90]. 

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Solids materials that are insoluble in hydrocarbon or water can be entrained in the crude. These are called bottom sediments and comprise fine particles of sand, drilling mud, rock such as feldspar and gypsum, metals in the form of minerals or in their free state such as iron, copper, lead, nickel, and vanadium. The latter can come from pipeline erosion, storage tanks, valves and piping systems, etc. whatever comes in contact with the crude oil. 

Very clean sands are rare and normally variable amounts of c/ay will be contained in the reservoir pore system, the clays being the weathering products of rock constituents such as feldspars. The quantity of clay and its distribution within the reservoir exerts a major control on permeability and porosity. Figure 5.2 shows several types of clay distribution. 

Carbonate reservoirs are usually affeoted to varying degree by diagenesis. However the process of dissolution and replacement is not limited to carbonates. Feldspar for instance is another family of minerals prone to early alterations. 

Aluminium is not found free but its compounds are so widespread that it is the most abundant metal in the earth s crust. Aluminosilicates such as clay, kaolin (or china clay), mica and feldspar are well known and widely distributed. The oxide. AI2O3. occurs (anhydrous) as corundum and emery, and (hydrated) as bauxite. Cryolite. Na,AlF. (sodium hexafluoroaluminate). is found extensively in Greenland. 

Silicon makes up 25.7% of the earth s crust, by weight, and is the second most abundant element, being exceeded only by oxygen. Silicon is not found free in nature, but occurs chiefly as the oxide and as silicates. Sand, quartz, rock crystal, amethyst, agate, flint, jasper, and opal are some of the forms in which the oxide appears. Granite, hornblende, asbestos, feldspar, clay, mica, etc. are but a few of the numerous silicate minerals. 

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... 

Aluminosilicates. These silicates consist of frameworks of silica and alumina tetrahedra linked at all corners to form three-dimensional networks familiar examples are the common rock-forming minerals quartz and feldspar. Framework silicates generally form blocky crystals, more isotropic... 

Alumina in combination with siUca is present in limestone chiefly as clay, though other aluminum siUcates in the form of feldspar and mica may be found. When present in appreciable quantities, clay converts a high calcium limestone into a mad or argillaceous stone, which when calcined yields limes with hydrauhc properties. Limestones containing 5—10% clayey matter yield feebly hydrauHc limes those containing 15—30% produce highly hydrauHc limes. 

Sihceous matter other than clay may occur in the free state as sand, quartz fragments, and chert, and in the combined state as feldspar, mica, talc (qv), and serpentine. Metallurgical and chemical limestones should contain less than 1% alumina and 2% siUca. 

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 %. 

The soft weathered granodiorite and pegmatites can vary in color from white to pink, depending on iron content and type of feldspar present. The mica content of these deposits ranges from 6—15% and varies in particle size from tiny (<44 specks to thumbnail size. Large books of mica that weigh several hundred kilograms have been found in these deposits. 

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. 

Sodium sihcate (41°Bh, 1 3.22 ratio Na20 Si02) is added in the milling operation to disperse the slime, mosdy kaolin. Dispersion also aids the grinding process. The rod mill serves to grind the ore to 0.833 mm (—20 mesh) or to the point where mica, quart2, feldspar, and iron minerals are Hberated. Cyclones, or rake, hydrauhc, or other types of classifiers, are used after grinding to produce coarse and fine mica fractions that are treated separately. 

The fine mica fraction is deslimed over 0.875—0.147-mm (80—100-mesh) Trommel screens or hydrocylcones, or is separated with hydrosi2ers. The deslimed pulp (<0.589 mm (—28 mesh)) of mica, feldspar, and quart2 is then fed to a froth flotation circuit where these materials are separated from each other either by floating in an acid circuit with rosin amine and sulfuric acid (2.5—4.0 pH), or an alkaline circuit (7.5—9.0 pH) with tall oil amine, goulac, rosin amine acetate, and caustic soda (see Eig. 2). 

The slime, consisting of kaolin, fine quart2, and feldspar, is sometimes used as is after being dewatered. This material may be used in the manufacture of light-colored brick or may be further processed to produce a high grade ceramic kaolin used in the manufacture of dinnerware, electrical porcelain, or sanitary-ware (see Ceramics). Floes of kaolin may be sold in bulk from the drier or pulveri2ed and sold in a powdered form. 

The main by-products of mica processiag plants are kaolin, quart2, and feldspar. Some plants produce all of these products for sale. 

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