Microcrystalline quartz

A heat-resistant, chemically inert form of microcrystalline quartz. A decorative material. Rare in industry. 

As noted already, Kuroko deposits are characterized by the following zonal arrangement in ascending stratigraphic order siliceous ore (quartz, chalcopyrite, pyrite), yellow ore (chalcopyrite, pyrite), black ore (sphalerite, galena, barite), barite ore (barite and quartz) and ferruginous chert ore (microcrystalline quartz, hematite). 

An agate is banded microcrystalline quartz (chalcedony). The bands are curved, and can be any color, opaque or translucent. 

Fossils that have been replaced with minerals are called pseudomorphs. This word means false form, referring to the specimen that has the form of one thing, but the composition of something else. Most fossil pseudomorphs are made of chalcedony (microcrystalline quartz). 

Chert is another organic marine sediment, less common than carbonate rocks, but found in huge deposits in some parts of the world. It initially consists of the skeletons of billions of tiny, single-celled animals called radiolaria. These skeletons are composed of microcrystalline quartz or chalcedony (Si02). Dense layers of this material accumulate on the ocean floor, where they are buried and compressed over time. The term chert is sometimes also applied to any compact, very fine-grained siliceous sediment that has resulted from precipitation or consolidation of silica gel. There may be chert lenses or very thin layers within other types of sediments, such as limestone. 

Framework - phyllosilicate/microcrystalline quartz fault rocks This class of fault rock is introduced here to describe fault rocks which form in sediments with concentrations (>20%) of dissolvable sponge spicules and varying amounts (15-40%) of phyllosilicates (Fig. 2d). Although not common, sediments with high sponge spicules contents are prone to the development of fault rocks by the cataclasis, dissolution and reprecipitation of silica. The process may be initiated by the collapse of secondary pores created by spicule dissolution and induce the redistribution of more soluble material by mixing. 

Quartz Properties Microcrystalline quartz, structure confirmed by XRD, BET specific surface area 6 m /g [429], external specific surface area used in calculations was 1.7 mVg [428,429],... 

SYNONYMS amorphous quartz, amorphous silica, cryptocrystalline quartz, fused quartz, fused silica, fuselex, microcrystalline quartz, quartz, glass, quartz sand, silicon dioxide, silicone dioxide, suprasil, vitreous silica. 

We made a maximum effort to ascertain that the boron in our analyses is indeed related to a siliceous phase. All samples were analyzed by X-ray diffraction, specifically searching for opal-CT peaks. All, but three samples are practically pure microcrystalline quartz. In three samples (marked by in Table 1), small opal-CT peaks were observed. The results for these samples should be viewed as possibly representing an admixture of opal-CT to quartz. All samples were examined under a scanning electron microscope both on a scale of 200 /a (field width) and 100 fi. On both scales, and at spot-counts, only Si and O peaks were observed (in some samples an Al peak slightly above background appeared). No cathodoluminescence is seen on aU examined cherts in the visible wavelength region. 

Photograph 10-10 Thin section of easily burned raw feed (45-pm fraction) composed largely of calcite fossil shells (foraminifera), many of which contain opaque crystals of pyrite (FeS ). Chert (microcrystalline quartz) with iron stain and dolomite at upper right, and large quartz at bottom. (S A6878)... 

Fukuda, J., Peach, C.J., Spiers, C.J. Nakashima, S. (2009a). Electrical impedance measurement of hydrous microcrystalline quartz. Journal of Mineralogical and Petrological Sciences, Vol. 104, pp. 176-181... 

Yamagishi, H., Nakashima, S. Ito, Y. (1997). High temperature infrared spectra of hydrous microcrystalline quartz. Physics and Chemistry of Minerals, Vol. 24, pp. 66-74... 

Microcrystalline quartz. See Silica, fused Microcrystalline wax CAS 8063-08-9 63231-60-7 64742-42-3 EINECS/ELINCS 264-038-1 INS905c(i) E905... 

Microcrystalline quartz Quartz glass Quartz sand Silica, amorphous fused Silica, crystalline fused... 

Pressure also has a marked effect on the rate of crystallization. Oehler (164b) found that silica gel crystallized to microcrystalline quartz (chert) even at 165 C at 3000 bars. 

It appears that most amorphous forms of silica that are generated in nature eventually crystallize to microcrystalline quartz, probably in less than a million years, thus becoming much less soluble and reactive. 

Seawater contains only 2-14 ppm of SiOj and is far below saturation with respect to amorphous silica (34). Part of this is suspended fragments of siliceous organisms (35). Siever has pointed out that the major mechanism for the predpitation of silica on the surface of the earth is biochemical (36). The various organisms responsible for silica deposition were reviewed by Voronkov, Zelchan, and Lukevits (4a). The microcrystalline quartz minerals jasper and chalcedony are probably transformation products of very early diatomite deposits. About two-thirds of the deposited silica is from diatoms and the remainder from radiolaria and sponges. 

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