Quartz grains

Cataclasis the fault movement has destroyed the rock matrix close to the fault plane. Individual quartz grains have been ground up creating a seal comprising of rock flour . 

We can see this point by evaluating the characteristic time required for chemical reaction to change the concentration of dissolved silica, and that required to affect the mass of quartz grains. These intervals are the relaxation times (s) for the groundwater and aquifer minerals (Lasaga and Rye, 1993 Lichtner, 1996). In... 

The reservoir rock in our model is composed of quartz grains, carbonate cement, and clay minerals in the following proportions, by volume ... 

Fig. 1.2 Electron Scanning Microscope picture of various quartz grains (Dress et al., 1989)...

The granite outcrops are medium- to coarse-grained and have a hypidio-morphic granular texture dominated by rounded or interlocking quartz grains, and laths of pink, white, and perthitic feldspars. 

Fig. 15.7 Glo bular goethite aggregates on quartz grains in a 20000 year old Quarternary sand deposit at Karup, Jutland, Denmark (Postma, Brocken-huus-Schack, 1987 with permission).

Another early use of iron oxides was as a cosmetic. The cosmetic boxes (cockleshells) found in the Royal Cemetery in the ancient Sumerian city of Ur contained a range of different colours. XRD analysis by the Research Department of the British Museum showed that the principal components of the red and yellow colours were hematite and goethite, respectively (Bimson, 1980). One box also contained a purple powder consisting of a mixture of quartz grains and large crystals of hematite. 

Plate 16.11 Coethite palisades around quartz grains in a ferricrete. Debal, Sudan (Schwarz 1992 with permission courtesy T. Schwarz)... 

Suppose there are many calcite grains and quartz grains in a rock. At each surface, there is interface reaction. For metamorphic reactions that take many years, mass transport in the fluid phase may be assumed to be rapid and the reaction rate is controlled by the interface reaction rate. The fluid composition may be regarded as uniform. At the surface of phase A (such as calcite), the interface reaction rate may be written as (Equation 4-34)... 

Optical bleaching sediment. Sunlight-reduced ESR signal intensity of the holes centres associated with A1 impurity and electron centres related to Ge impurities in quartz grains (sand). Whether sunlight bleached the optically sensitive centres completely is an issue in dating of sediments.45... 

High rates of water influx remove SiO at low solution concentrations. Normal ground water and streams carry about 17 ppm SiO and less in high rainfall areas (Davis, 1964). In some weathering profiles silicification or deposition of silica has been observed. Most often the form of the phase deposited is crypto-crystalline, either opal or chalcedony. In these cases quartz grains do not show overgrowths (Elouard and Millot,... 

Corroded quartz grains have been reported in association with chert in modern carbonates (Bartholome, 1966), and they are known to occur in sand and salt deposits (Dapples, 1959, 1962 Braitsch, 1971). Chalcedony is found associated with quartz in marine sediments formed from devitri-fied glass (Muller, 1961). Amorphous silica is common in recent ocean sediments (Biscaye, 1965 High and Picard, 1965 Calvert, 1971) and has also been identified in deltaic terriginous sediments (Millot, 1964). 

Examples have been reported where quartz overgrows quartz grains and the interstitial spaces are filled with chalcedony (Kautz, 1964), but... 

Although experiments indicate an instability of 7 8 magnesian chlorite and quartz, it is common to find chamosite pellets with a quartz grain at their center (Schellmann, 1969). Does this mean stability due to a high iron content, poor experimental data, or a metastable association ... 

BARTHOLOME (P.), 1966a. Corroded quartz grains in sedimentary ores of iron and manganese. Econ. Geol., (II, 886-96. 

Vickers hardness determination with correction for degree of brittleness and converted to hardness classes, compared with quartz grain dynamic abrasion hardness, for example, of microcrystalline steatitic ceramics... 

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