Gneiss

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. 

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). 

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). 

Fossil slates, schists, gneiss, igneous rocks 2000 1000 upwards - -... 

In the late 1960s El Goresy and Donnay [17] discovered a new form of carbon which they called white carbon or Chaoite in a carbon-rich gneiss in the Ries meteorite crater in Bavaria. Chaoite has an hexagonal crystal stmcture and it... 

Graphite is widely distributed throughout the world though much of it is of little economic importance. Large crystals or flake occur in metamorphosed sedimentary silicate rocks such as quartz, mica schists and gneisses crystal size varies from <1 mm up to about 6 mm (average 4mm) and the deposits form lenses up to 30 m thick stretching several... 

Some of the complications involved in multi-scale porosities and evolutionary paths within fractured rock systems have been explored. For example, in the Palmottu site of gneisses in Finland U, as well as Th, was found to be redistributed into fracture coatings of carbonates and Fe oxides (Suksi et al. 1991). Suksi and Rasilainen (1996) have demonstrated how U concentrated in these fracture fillings can implant daughters in the surrounding phases, generating large fractionations between and Th/ U. 

Soil is a mixture of solid materials, air and, usually, water and organic matter. The radium content of soil often reflects that of the rocks from which the solid materials are derived by physical and chemical activity. The observed ranges are from 0 to 20 Bq kg for ultrabasic rocks (dunite) to 1 to 1835 Bq kg for igneous metamorphic rocks (gneiss) (Wollenberg, 1984). While these ranges are broader than those for measured for soils, the mean values for rocks, excluding alkali rocks, is consistent with the means observed for soils. 

Meteorites present an opportunity to look at geological time or the time told by radionucleotides within rocks. The oldest rocks found on Earth are not as old as the age of the Earth due to continual reprocessing of the Earth s surface. The oldest discovered rocks so far are the Acasta gneisses from Northwestern Canada, which are 4.03 Gyr, but these are young compared with the CAIs found in the Allende meteorite, which are 4.566 0.002 Gyr or 4.556 billion years. The ages of these species are derived from the relative abundances of radioisotopes and their daughter species, as seen in Table 6.3. 

Crowflight Minerals Inc. The ore deposit consists of Aphebian ultramafic sills intruded into Archean gneisses (Wardrop 2008). Rougher tails were produced from lock cycle testing of bulked drill core samples. 

Detectior limits Acidic rock Inter- mediate rook Basic rook Ultra- mafic rook Sand- stone Shale Carbo- nate Gneiss Leptite Amphi- bolite Meta- pelite Vlarble Alluvial plain soils Soils Stream Sedi- ments Shallo w sea Sed- iments... 

Figure 9. Exposure pathways based on the averaged coefficients ofbiogeochemical uptake, Cb, of trace metals in Spruce Forest ecosystems of the Karelia top scheme represents the ecosystem with Podzols on diabase outcrops and bottom scheme represents the ecosystem with Podzols on gneiss outcrops. 1—spruce needles 2—spruce bark 3—hypnic mosses 4—leaves and twigs of blueberry (based on Dobrovolsky, 1994).

The hybrid magma contains proportions of gneiss and basalt in a ratio of 4 to 7. >... 

Table 1.6. Calculated Sr concentrations (ppm) and87SrIs6Sr ratios for different fractions of gneiss in the hybrid rock.

Figure 1.5 The linear array of mixing between gneiss and basalt in a plot of 87Sr/86Sr vs the reciprocal of Sr concentration [equation (1.3.8)]. Data from Tablel.6.

Draw in a diagram Na20/CaO vs FeO/MgO, the curve representing the hybrids (mix = hyb) between a basalt (a = bas) and a gneiss (fi=gn), whose compositions are listed in Table 1.7a. Discuss the relationship between CaO and the magnesium number mg which is the atomic ratio Mg/(Fe + Mg)... 

Table 1.7c. Results of the mixing calculation shown in Figure 1.6 for selected values of gneiss...

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