Feldspars abundance

Figure 6. Abundance of feldspar as summarized from original petrographic data. Key 1, < 3 percent 2, 3-4 percent 3, 4-6 percent and 4, 6 percent. Feldspar abundance is expressed as...

Figure 1. Plot of thermoluminescence sensitivity against petrologic type (5,6), which reflects the degree of metamorphic alteration 3, least metamorphosed 6, most metamorphosed. The feldspar scale is calculated on the assumption that the TL sensitivity is directly proportional to feldspar abundance and type 5,6 chondrites typically contain about 8% of this mineral. The cross-hatched region refers to TL sensitivity levels at which the feldspar is thought to be in the low-temperature ordered form (see Figure 13). The symbols refer to the three data sources (6,8,14). (Reprinted by permission from Ref. 31.

In Michigan, feldspar content, as a fraction of total mineral content, is approximately half of that in the Mid-Sweden chronosequence. In contrast, the fraction of tunnelled feldspars in the Michigan chronosequence is twice that of the Mid-Sweden chronosequence. That could indicate that tunnelling is driven by nutrient demand. But, if the data are corrected for the difference in feldspar content, to get the fraction of tunnelled minerals, both curves match (Fig. 13.2). This suggests that feldspar tunnelling activity is independent of feldspar abundance, and could be determined by EM density. Indeed, a positive correlation was found between the frequency of tunnelled feldspars and EM density (Hoffland et al, 2003). 

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. 

Potassium and sodium share the position of the seventh most abundant element on earth. Common minerals such as alums, feldspars, and micas are rich in potassium. Potassium metal, a powerful reducing agent, does not exist in nature. 

Aluminum [7429-90-5] Al, atomic number 13, atomic weight 26.981, is, at 8.8 wt %, the third most abundant element in the earth s cmst. It is usually found in siUcate minerals such as feldspar [68476-25-5] clays, and mica [12001 -26-2]. Aluminum also occurs in hydroxide, oxide—hydroxide, fluoride, sulfate, or phosphate compounds in a large variety of minerals and ores. 

Indium (0.24 ppm) is similar in abundance to Sb and Cd, whereas T1 (0.7 ppm) is close to Tm and somewhat less abundant than Mo, W and Tb (1.2 ppm). Both elements are chalcophiles (p. 648), indium tending to associate with the similarly sized Zn in its sulfide minerals whilst the larger T1 tends to replace Pb in galena, PbS. Thallium(I) has a similar radius to Rb and so also concentrates with this element in the late magmatic potassium minerals such as feldspars and micas. 

The structural complexity of the 3D framework aluminosilicates precludes a detailed treatment here, but many of the minerals are of paramount importance. The group includes the feldspars (which are the most abundant of all minerals, and comprise 60% of the earth s crust), the zeolites (which find major applications as molecular sieves, desiccants, ion exchangers and water softeners), and the ultramarines which, as their name implies, often have an intense blue colour. All are constructed from Si04 units in which each O atom is shared by 2 tetrahedra (as in the various forms of Si02 itself), but up to one-half of the Si... 

The feldspars are aluminosilicates in which as much as half the silicon(IV) has been replaced by aluminum(III). They are the most abundant silicate materials on Earth and are a major component of granite, a compressed mixture of... 

MacKenzie and Garrels equilibrium models. Most marine clays appear to be detrital and derived from the continents by river or atmospheric transport. Authigenic phases (formed in place) are found in marine sediments (e.g. Michalopoulos and Aller, 1995), however, they are nowhere near abundant enough to satisfy the requirements of the river balance. For example, Kastner (1974) calculated that less than 1% of the Na and 2% of the K transported by rivers is taken up by authigenic feldspars. 

Feldspar type of clay. Some clay deposits may include appreciable amounts of quartz. Commercial grades of clays may contain up to 20% quartz. Most abundant group of materials, composed of silicates of aluminium with sodium, potassium, calcium, and rarely barium. Most economically important mineral. Used for ceramics, glass, abrasive wheels, cements, insulation and fertilizer. 

Feldspars are the most abundant minerals of igneous and metamorphic rocks 0 2). Being the most abundant rock-forming minerals of the earth s crust, they have received a proportionately large share of attention from students of weathering, and most of the major analytical advances and conceptual models which have been applied to other mineral groups have also been applied to feldspars. 

Part of this program was realized at the Survey. Between 1901 and 1907, the chemist Allen, the physicist Day, and the petrographer, Iddings, completed a rigorous study of the thermal properties of the plagioclase feldspars, the most abundant rockforming minerals. This study was important in several respects. 

Occurrence. Silicon is the second most abundant element in the earth s crust, after oxygen (about 28% by weight). It occurs mainly in oxides (quartz, agate, opal, etc.) and a great variety of silicate minerals (feldspar, clay, mica, olivine, etc.). 

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. 

The rocks of the NS-N dyke group range from nepheline syenite to sodalite-bearing nephelinolite. The primary phases in the NS-N dyke group are k-feldspar and nepheline, with variable abundances of amphibole, plagioclase, phlogopite, calcite, sodalite, titanite, cancrinite, apatite, clinopyroxene, zircon, chlorite, quartz, pyrochlore, and opaque phases. 

---