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Quartz

Silica, Flint

Chemistry

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Links to Other Materials

Amorphous Silica - Related
Cristobalite - Related
Silica - Related
Flint - Related
Cache

Hazards

Quartz, Crystalline Silica

Miscellaneous

Family: Silica
Region: North America
Mined At: Unspecified
Raw Mineral: No
Generic: Yes

Notes

Quartz is silica mineral. White or milky quartz is an opaque white, greasy-looking and sharply angular very hard rock. "Quartz" is actually one of many phases of silica. All other phases are very rare in comparison.

Crystalline silica is a compound of the elements silica and oxygen and it is a primary component in most of the minerals and rocks found in earth's crust. When the basic structure of the molecule is a pattern that is repeated and symmetrical, the silica compound is said to be "crystalline".

It is found in most rocks. Natural geological processes by decomposed the earth's rock crust to form gravels, sands and soils. Thus crystalline silica compounds are found virtually everywhere on the surface of the earth.

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.

Amethyst is a variety of quartz.

See also Silica Placing Sand, Flint, Silica, Cristobalite, Amorphous Silica, Fused Silica.

(Richard Willis)

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.

Data

Melting Point (MP): 1710C M
Specific Gravity: 2.65

Linked Articles

Dealing With Dust in Ceramics
A checklist of for changes and additions to your tools and equipment and suggestions for habit changes you need to make to control dust
Quartz Toxicity
Quartz is one of the most dangerous materials used in ceramics, yet it is the most abundant, irreplacable, we must learn to use it safely.
SILICOSE et DÉPISTAGE - Edouard Bastarache
SILICOSE et DÉPISTAGE - Edouard Bastarache
SILICOSIS and SCREENING by Edouard Bastarache
SILICOSIS and SCREENING by Edouard Bastarache