Quartz crystallised

Hydrothermal crystallisation processes occur widely in nature and are responsible for the formation of many crystalline minerals. The most widely used commercial appHcation of hydrothermal crystallization is for the production of synthetic quartz (see Silica, synthetic quartz crystals). Piezoelectric quartz crystals weighing up to several pounds can be produced for use in electronic equipment. Hydrothermal crystallization takes place in near- or supercritical water solutions (see Supercritical fluids). Near and above the critical point of water, the viscosity (300-1400 mPa s(=cP) at 374°C) decreases significantly, allowing for relatively rapid diffusion and growth processes to occur. 

Matsuhisa J, Goldsmith JR, Clayton RN (1978) Mechanisms of hydrothermal crystallisation of quartz at 250 C and 15 kbar. Geochim Cosmochim Acta 42 173-182... 

It is interesting that GeOj, with p 0.43, crystallises with both the rutile and the quartz structure. 

At the onset of biomineralization the mechanism of phosphate and silica deposition is essentially the same. Both start with a highly hydrated amorphous phase having glass-like physical-chemical properties. The kinetics of crystallisation of the two differs. ACP will rapidly alter in the direction of apatite in hours or days, whereas amorphous silica requires thousands of years or higher temperatures to yield quartz. 

The first minerals to crystallise, at highest temperatures and pressures, are poor in silicon (<50% Si02) and are rich in calcium, iron and magnesium and they form minerals, such as olivine and the pyroxenes, which make up the basic or mafic rocks. The acidic or silicic rocks are the last to form, are rich in silicon (>65% Si02) and are dominated by quartz, the potash feldspars and muscovite. 

GaP04 is similar to AIPO4 in being able to crystallise in stmctural forms related to the silica polymorphs quartz and cristobalite. The Ga NMR spectra of both GaP04 structures have been recorded, the NMR parameters (Table 10.4) being consistent with the more symmetrical tetrahedral Ga environment in the cristobalite form (Massiot et al. 1999). 

Hydrogen peroxide [7722-84-1] M34.0, df 1.110, pK 11.65. The 30% material has been steam distilled using distilled water. Gross and Taylor [J Am Chem Socll 2075 7950] made 90% H2O2 approximately O.OOIM in NaOH and then distilled it under its own vapour pressure, keeping the temperature below 40°, the receiver being cooled with a Dry-ice/isopropyl alcohol slush. The 98% material has been rendered anhydrous by repeated fractional crystallisation in all-quartz vessels. EXPLOSIVE IN CONTACT WITH ORGANIC MATERIAL. 

In order to achieve SPP excitation, the light must be incident at the inner surface of the crystal near the critical angle and be p-polarised [39]. The applied potential was modulated by 50 mV either side of the point of zero charge of the evaporated/partially crystallised gold layer on a quartz internal reflectance crystal. 

This is a very abundant mineral, occurring chiefly in veins along with lead ore, heavy spar, and quartz. It is well known as fluor, or Derbyshire spar, and crystallises beautifully in cubes, octahedrons, and tetrahedrons, which are transparent and colourless, or purple, green, brown, or yellow. It also occurs in a massive semicrystalline form, capable of being cut and... 

Chemical vapour deposition (CVD), or more specifically, organo-metallic CVD can also be used to prepare ferrite thin films (Itoh, Takeda Naka, 1986). A mixture of acetylacetonate complexes of the desired metal is evaporated in a quartz boat (number 1 in Fig. 3.27) and is reacted with O2, which is introduced directly in the deposition zone. By adding a second furnace (B), an additional component evaporating at a different temperature can be transported to the substrate. Glass or MgO single crystals can be used as the substrates an annealing up to 1(X)0°C is performed on the film to improve its crystallisation. Spinel thin films (Ni, Ni-Zn) have been prepared by this method. 

Ge is directly below Si in the periodic table, and both SiOi and GeOz may crystallise as quartz, cristobalite and rutile phases. This tetravalent atom can adopt coordination numbers of 4-6 in contrast to Si that is normally tetrahedral in its oxides, therefore, it is not surprising that Ge substitution into several zeolite frameworks including THO, FAU, LTA and PHI topologies was successfully attempted five decades ago. Until the late 1990s, however, no attempts to synthesise new microporous germa-nate frameworks in which all Ge atoms are tetrahedral had been successful.f " " ... 

TABLE 11-2 Phase components in dependence on the concentration of PDDA-Cl (P40) and on the crystallisation time. The crystallization temperature is 175 C. The composition of the reaction mixture is 4 Na O 1 AljOj 40 SiOj 1200 H2O x PDDA-Cl. The phase component were denoted as a amorphous, MFl zeolite MFI, Mo mordenite, SH-P40 novel layer silicate, Ke kenyaite-like silicate, Cr cristobalite, and Q quartz. 

Fig. 155. Macrophages in the marginal zone of the splenic white pulp of a male white rat (No. 30) 8 weeks after an intravenous application of 25 mg Brazilian crystallised quartz (specific surface 2 mVg). Fixed by immersion in Bouin s fluid. Paraplast. Azan modification using rubine fast rea and aniline blue (Specht 1973). Objective Leitz Pi 40/0.65. Leitz-Orthomat (x3.2). Elliptic polarised light. Agfachrome 50 L professional...

The essential instability of some metal film-solid systems may be shared by films of organic and inorganic solids, which crystallise readily. The observations on metal films are, however, more numerous, and their behaviour has been studied on surfaces of metals, mica, quartz, and diamond. 

Intrinsically fillers can be divided into two types, reactive and inert. Reactive fillers will react with their environment. A good example of this is gibbsite (aluminium hydroxide), which will react with both acidic and basic substances. Aluminium hydroxide also loses its water of crystallisation at around 200 °C and this enables it to provide fire retardancy in polymer formulations. The silicate minerals (kaolin, mica, talc, quartz, etc.), are, in classical chemical terms, virtually inert, only being attacked by very strong acids and alkalis. The carbonate minerals and the hydroxide minerals are very reactive to acids. 

Igneous rocks are formed by the cooling and solidification of a molten rock mass. During cooling, ordered crystallisation occurs. However, minerals may be formed not only by crystallisation, but may also result from reactions between already formed minerals and molten ingredients. Minerals may be formed throughout a rock, concentrated in certain areas, or in very localised veins or strata. The bulk of the silicates such as kaolin, mica, talc, feldspar, wollastonite and quartz are all found in igneous rocks. 

This method has been suceessfully used to synthesise a lithium aluminosilicate geopolymer, which is difScult to prepare by the conventional method because of the poor solubility and weak alkalinity of LiOH solution. In this solid stale synthesis , halloysite clay was reacted with LiOH at S50°C. When wetted, the product of this solid state reaction sets at 40°C to a compound containing solely 4-fold coordinated A1 and a typical Si MAS NMR spectrum (Figure 5), but is not fully X-ray amorphous . When heated at 900 C, this geopolymer crystallises to o-eucryptite, LiAISi04 but if additional quartz is added, heating at 1300 C for 8hr causes the crystallization of p-eucryptite and P-spodumene (LiAlSi206) . 

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