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Formula: SiO2
Chemistry %
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| DENS - Density (Specific Gravity) | 2.65 |
| MLPT - Melting Point (MP) | 1710C M |
Unlike silica glass, the quartz phase of silica is subject to inversion and accompanying volume and form change when fired through 573C. Room temperature quartz is called alpha quartz, beta quartz exists only above 573C.
Quartz sand is often used in bodies as grog for texture and to increase thermal expansion. Powdered quartz is used in glazes and bodies also. Quartz of very fine particle size (-400 mesh) will typically enter the feldspathic melt or convert to cristobalite during firing if fluxes are lacking, coarse powdered grades help to 'squeeze' glazes into fit. Intermediate sizes (200-300 mesh) seem to be best however, since their greater surface area exerts more compressive squeeze per unit.
Crystalline silica is used in agriculture, paving, brick and tile, concrete, cleansers, foundry casting, ceramics and pottery, paint, glass, soaps, fiber glass, electronics, plaster, sandblasting, industrial effluent filtration, drinking water filtration, hazardous waste control.
Mineral, of the ideal form SiO2 with a typical empirical analysis of SiO2 100%
Hardness: 7 Density: 2.65 Soluble in HCl
There are two major groupings of quartz, and varieties are denominated according to color/opacity:
phanero-crystalline: crystals visible to the naked eye, such as:
“rock crystal” = clear; “amethyst” = violet; “smoked” = tan; “pink” = pink; “morion” or “black” = black; “citrine” = lemon yellow; “blue” = blue; “tiger-eye” = (can be cut to look like) a tiger’s eye; “falcon-eye” = (... like) a falcon’s eye; “cat-eye” = (...like) a cat’s eye; (the “... eye” quartzes being pseudo-morphic); “Aventurine” = visible mica
and/or hematite inclusions; “common” = grey; “milky” = white; “ferrous” = visible iron deposits, etc.
crypto-crystalline: crystals visible through a microscope, such as chalcedony.
In contrast to the SiO2 of hydrous aluminum silicates, such as the feldspars and kaolins, the SiO2 of quartz is in its orderly (geometrically, uniformly, aligned — “morphic”) more matured, crystalline form: practically speaking, it is more given to the infamous “quartz-splitting” than is a feldspar silica.
Splitting is less a concern with glaze coverings than with fabric bodies. When glaze crackling or crazing is desired, for example, quartz’s inclination to split is a benefit. Subsequently, glaze recipes call for quartz much more frequently than do body fabric recipes. Fabrics (clay “bodies”) normally get their SiO2 from the silicas already comprising the clays being used (kaolin, feldspars, earthenware clays, etc.) and are calculated accordingly.
see refs to cristobalite, clay, feldspar, flint, glaze, silica, etc.
Out Bound Links
The main crystalline mineral form of silica. White...
In Bound Links
Silicon dioxide, silica, quartz
Quartz
A measure of the reversible volume or length chang...
This term refers to an abrupt 2% change in volume ...
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