Granites

Aluminum can now be produced from clay, but the process is not economically feasible at present. Aluminum is the most abundant metal to be found in the earth s crust (8.1%), but is never found free in nature. In addition to the minerals mentioned above, it is found in granite and in many other common minerals. 

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. 

The lanthanides, distributed widely in low concentrations throughout the earth s cmst (2), are found as mixtures in many massive rock formations, eg, basalts, granites, gneisses, shales, and siUcate rocks, where they are present in quantities of 10—300 ppm. Lanthanides also occur in some 160 discrete minerals, most of them rare, but in which the rare-earth (RE) content, expressed as oxide, can be as high as 60% rare-earth oxide (REO). Lanthanides do not occur in nature in the elemental state and do not occur in minerals as individual elements, but as mixtures. 

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 %. 

Quartz-Pebble Conglomerate Deposits. Known quartz-pebble conglomerate ores are restricted to a specific period of geologic time. These ore types occur in basal Lower Proterozoic beds unconformably situated above Archaean basement rocks composed of granitic and metamorphic strata. A number of commercial deposits are located in Canada and South Africa. Some subeconomic occurrences have been reported in Brazil and India... 

Intrusive Deposits. Deposits included in the intmsive deposit type are those associated with intmsive or anatectic rocks of different chemical composition, eg, alaskite, granite, monzonite, peralkaline syenite, carbonatite, and pegmatite. Examples include the uranium occurrences in the porphyry copper deposits such as Bingham Canyon and Twin Butte in the United States, the Rossing Deposit in Namibia, and Ilimaussaq deposit in Greenland, Palabora in South Africa, and the deposits in the Bancroft area, Canada (15). 

Meta.soina.tlte Deposits. Included in the metasomatite deposit grouping are uranium deposits in alkah metasomatites, eg, albitites, aegirinites, and alkah—amphibole rocks, commonly intmded by microcline granite. Examples are the deposits in Espinharasin, Brazil, and Ross Adams, Alaska, as well as the Zheltye Vody deposit in Krivoy Rog area in Ukraine (16). 

Occurrence and Recovery. Rhenium is one of the least abundant of the naturally occurring elements. Various estimates of its abundance in Earth s cmst have been made. The most widely quoted figure is 0.027 atoms pet 10 atoms of silicon (0.05 ppm by wt) (3). However, this number, based on analyses for the most common rocks, ie, granites and basalts, has a high uncertainty. The abundance of rhenium in stony meteorites has been found to be approximately the same value. An average abundance in siderites is 0.5 ppm. In lunar materials, Re, when compared to Re, appears to be enriched by 1.4% to as much as 29%, relative to the terrestrial abundance. This may result from a nuclear reaction sequence beginning with neutron capture by tungsten-186, followed by p-decay of of a half-hfe of 24 h (4) (see Extraterrestrial materials). 

Other important uses of stannic oxide are as a putty powder for polishing marble, granite, glass, and plastic lenses and as a catalyst. The most widely used heterogeneous tin catalysts are those based on binary oxide systems with stannic oxide for use in organic oxidation reactions. The tin—antimony oxide system is particularly selective in the oxidation and ammoxidation of propylene to acrolein, acryHc acid, and acrylonitrile. Research has been conducted for many years on the catalytic properties of stannic oxide and its effectiveness in catalyzing the oxidation of carbon monoxide at below 150°C has been described (25). 

Tungsten deposits occur in association with metamorphic rocks and granitic igneous rocks throughout the world (Table 2). Deposits in China constitute over half of the world reserves and over five times the reserves of the second largest source, Canada. 

Ragnar A. Granit medicine, physiology research which illuminated electrical properties of vision by studying wavelength discrimination by eye... 

Zirconium occurs naturally as a siUcate in zircon [1490-68-2] the oxide baddeleyite [12036-23-6] and in other oxide compounds. Zircon is an almost ubiquitous mineral, occurring ia granular limestone, gneiss, syenite, granite, sandstone, and many other minerals, albeit in small proportion, so that zircon is widely distributed in the earth s cmst. The average concentration of zirconium ia the earth s cmst is estimated at 220 ppm, about the same abundance as barium (250 ppm) and chromium (200 ppm) (2). 

Materials that come in contact with wet halogens must be corrosion-resistant. Glass, ceramics, tantalum, and fiuoropolymers are suitable materials. Granite has been used in steaming-out towers. 

P. Cemy, Short Course in Granitic Pegmatites in Science and Industry, Mineralogical Association, Winnipeg, Canada, 1982, p. 150. 

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