Quartz deposition

Quarz-keil, m. (Optica) quartz wedge, -kiesel, m. quartz gravel, -kristall, m. quartz crystal, rock crystal. -lager, n. quartz deposit, -linse, /. quartz lens, -mehl, -pulver, n. quartz powder- -rohr, n., -rohre, /. quartz tube, -sand, m. quartz sand, -scheibe, /. 

Quartz deposition in a fracture 26.2 Quartz deposition in a fracture... 

Bendigo is a classic example of a low-sulphide gold-quartz deposit located in a folded sequence of sandstone and shale of the Cambrian-Ordovician age (Ramsay et al. 1998 Goldberg et al. 2007). Regional soil geochemistry covers an area of 4,000 km. Sampling Grid 5x5 km. 134 samples were collected as can be seen in Fig. 2, titanium anomalies form sub-... 

The 5 0 values for vein-forming fluids for the two areas sampled are assessed using the A 0 (quartz-H20) and inferred temperature of vein formation (350-400°C Fig. 1). The range of 5 Oh2o values Is +9 to +12%o for quartz deposition at 350-400°C. An alternative Interpretation Is that the variation In 5 Oquartz reflects deposition from a fluid of uniform 5 0, but over a temperature range of about 50°C, as constrained by 5 Oquartz values it is not possible to discriminate between these models. Regardless, the vein fluids had a... 

Higgins 1985). Aithough it may not be especiaiiy iarge, the Grey River deposit was once described as one of the iargest typicai wo ifra mite-quartz deposits in Canada , and it is possibiy indicative of much wider potentiai for W in the generai area. 

Ultrastructural patterns that arise when amino acids or small peptides interact with mineral surfaces have been studied in some detail99,100). A poly-L-alanine solution evaporated at 40 °C on a rhombohedral plane of R-quartz deposits the peptide principally in a-conformation. Chain-folded helices are aligned in the form of lamellae which exhibit a sharp phase boundary at the organic-mineral contact zone (Fig. 9). Frequently the lamellae are split along the direction of their fold axis ("zipper effect ). Insertion of 0-pleated sheets running perpendicular to the long axis of the lamellae act as dispersion forces and cause the formation of cross-0-... 

Quartz is the dominant form in which silica is found in coals, and it is ubiquitous. There is some distinction between clastic grains of quartz introduced by wind or water and authigenic quartz deposited from solutions. Quartz is also a major component of clay and siltstone partings in coal that are of detrital origin. 

In Figure 1, the infrared absorbance spectrum of a blank MSA filter, a, is compared directly with that of a prepared standard filter, b, with 100 micrograms of 15 micron Min-U-Sil quartz deposited on it. To determine the absorbance of the 800 cm peak it is necessary to approximate a baseline as indicated by the dotted line of spectrum As an indication of sensitivity the... 

Example 2.7 It is necessary to determine partition coefficients in quartz deposits with porosity 0.2, which include clays 0.5% and organic carbon 0.1%. The deposits are saturated with fresh water with Ca + concentration 2 mmoleT F... 

The quartz geothermometer (Fournier, 1977) requires that the dissolved silica concentration in an ascending hydrothermal solution becomes quenched in as the fluid approaches the surface. On the other hand, the phase transfer model for the rate of quartz deposition, described in this chapter, requires that the LEA be valid. The conditions for which each of these models is appropriate can be found by calculating values of Da, and Pe. Figure 8.1 shows the temperature range for the transition from LEA to quenched conditions. 

Ceramic processing occurs through some sequential activities, which starts with raw materials, proceeds through batch preparation and forming and concludes with firing. The sequence of steps is illustrated by Fig. 8.7. Ceramics are formed from raw materials used for traditional ceramics which are different from those used for advanced ceramics. For traditional ceramics raw materials consist of silica, clay, fluxes and are refractory materials. Silica is obtained either from massive quartz deposit or pure quartz sands. The quartz is washed and groimd. The most commonly used clay minerals are kaolin and talc. China clay is predominantly kaolin. Ball clays are finer particle size elays that contain... 

Quartz crystals are now produced synthetically to satisfy commercial demand. First, silica is dissolved under pressure in a hot, aqueous solution of sodium hydroxide then a small seed crystal of quartz is added. As the solution cools, quartz deposits from the saturated solution onto the seed crystal to form a large crystal. 

The main component of sandstone reservoirs ( siliciclastic reservoirs ) is quartz (Si02). Chemically it is a fairly stable mineral which is not easily altered by changes in pressure, temperature or acidity of pore fluids. Sandstone reservoirs form after the sand grains have been transported over large distances and have deposited in particular environments of deposition. 

Chemical properties of deposited monolayers have been studied in various ways. The degree of ionization of a substituted coumarin film deposited on quartz was determined as a function of the pH of a solution in contact with the film, from which comparison with Gouy-Chapman theory (see Section V-2) could be made [151]. Several studies have been made of the UV-induced polymerization of monolayers (as well as of multilayers) of diacetylene amphiphiles (see Refs. 168, 169). Excitation energy transfer has been observed in a mixed monolayer of donor and acceptor molecules in stearic acid [170]. Electrical properties have been of interest, particularly the possibility that a suitably asymmetric film might be a unidirectional conductor, that is, a rectifier (see Refs. 171, 172). Optical properties of interest include the ability to make planar optical waveguides of thick LB films [173, 174]. 

Monolayers can be transferred onto many different substrates. Most LB depositions have been perfonned onto hydrophilic substrates, where monolayers are transferred when pulling tire substrate out from tire subphase. Transparent hydrophilic substrates such as glass [18,19] or quartz [20] allow spectra to be recorded in transmission mode. Examples of otlier hydrophilic substrates are aluminium [21, 22, 23 and 24], cliromium [9, 25] or tin [26], all in their oxidized state. The substrate most often used today is silicon wafer. Gold does not establish an oxide layer and is tlierefore used chiefly for reflection studies. Also used are silver [27], gallium arsenide [27, 28] or cadmium telluride wafer [28] following special treatment. 

The principal ore of lead is galena, PbS. Although there are some galena deposits in Great Britain, much of this country s requirements must be imported. In the extraction of lead, the sulphide ore is first roasted together with quartz in a current of air ... 

P. Bachmann, P. Geitner, H. Hydton, G. Ronanowski, and M. Thelen, "Preparation of Quartz Tubes by Centrifugal Deposition of SUica... 

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... 

Phosphates are the principal catalysts used in polymerization units the commercially used catalysts are Hquid phosphoric acid, phosphoric acid on kieselguhr, copper pyrophosphate pellets, and phosphoric acid film on quartz. The last is the least active and has the disadvantage that carbonaceous deposits must occasionally be burned off the support. Compared to other processes, the one using Hquid phosphoric acid catalyst is far more responsive to attempts to raise production by increasing temperature. 

Acoustic Wave Sensors. Another emerging physical transduction technique involves the use of acoustic waves to detect the accumulation of species in or on a chemically sensitive film. This technique originated with the use of quartz resonators excited into thickness-shear resonance to monitor vacuum deposition of metals (11). The device is operated in an oscillator configuration. Changes in resonant frequency are simply related to the areal mass density accumulated on the crystal face. These sensors, often referred to as quartz crystal microbalances (QCMs), have been coated with chemically sensitive films to produce gas and vapor detectors (12), and have been operated in solution as Hquid-phase microbalances (13). A dual QCM that has one smooth surface and one textured surface can be used to measure both the density and viscosity of many Hquids in real time (14). 

Solubility. An important aspect of sihca chemistry concerns the sihca— water system. The interaction of the various forms of sihca with water has geological significance and is apphed in steam-power engineering where the volatilization of sihca and its deposition on turbine blades may occur (see Power generation), in the production of synthetic quartz crystals by hydrothermal processes (qv), and in the preparation of commercially important soluble sihcates, coUoidal sihca, and sihca gel. 

In the absence of a suitable soHd phase for deposition and in supersaturated solutions of pH values from 7 to 10, monosilicic acid polymerizes to form discrete particles. Electrostatic repulsion of the particles prevents aggregation if the concentration of electrolyte is below ca 0.2 N. The particle size that can be attained is dependent on the temperature. Particle size increases significantly with increasing temperature. For example, particles of 4—8 nm in diameter are obtained at 50—100°C, whereas particles of up to 150 nm in diameter are formed at 350°C in an autoclave. However, the size of the particles obtained in an autoclave is limited by the conversion of amorphous siUca to quartz at high temperatures. Particle size influences the stabiUty of the sol because particles <7 nm in diameter tend to grow spontaneously in storage, which may affect the sol properties. However, sols can be stabilized by the addition of sufficient alkaU (1,33). 

In an attempt to stimulate onshore production of synthetic quartz and piezoelectric devices in the 1970s, Brazil imposed an embargo on exports and ultimately raised the price several-fold for small quartz crystals used as the starting material for quartz growth. However, sources of suitable pure quartz were located in the United States and Canada, including vein and pegmatic deposits (1). Synthetic processes compatible with the natural U.S. quartz starting material from a variety of sources were developed, and U.S. production became relatively independent of imports (1). 

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