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Quartz

Quartz is the most abundant mineral on earth, it is the main crystalline mineral form of silica (SiO2). Natural deposits of relatively pure quartz are plentiful and grains of it are found in many other types of rocks and in most silts, soils and clay. White or milky quartz is an opaque white, greasy-looking, sharply angular very hard rock. Pure quartz melts at 1713C, far beyond the range of an average pottery or industrial production kiln.

Quartz is a fascinating study in the importance of considering the mineralogy of materials (as opposed to their chemistry). For example, quartz and fused silica glass have the same chemistry, 100% SiO2. But they have dramatically different physical properties (e.g. thermal expansion, hardness, specific gravity, melting temperature). To illustrate, consider diamond and graphite: they have the same chemistries. But they have radically different physical presences.

From a theoretical perspective, quartz is a mineral. However, in ceramics, it is also considered a material, often simply called "silica" (however original container bags often label it as "ground quartz"). Huge quantities of quartz powder are used in ceramic bodies and glazes. In bodies the quartz particles most often remain unchanged in the fired matrix, behaving as an embedded aggregate. They act as a "skeleton" in porcelain bodies. They raise the thermal expansion and make it easier to fit glazes. However, in glazes, the quartz particles dissolve in the glass and become a part of its chemical structure (thus the original properties of the quartz are gone, giving way to the new physical presence of the glass). The term "silicate" refers to minerals or fired materials where SiO2 predominates in the inventory or molecules that make up its structure. Kaolin is a silicate. In kaolin crystals, there are 2 molecules of SiO2 for every one of Al2O3. They combine chemically to form the familiar flat, stop-sign shape.

Quartz is the mineral form of silica powder used in ceramic glazes and clay bodies. It is the mineral that silica "wants to be" when cooled from molten to solid (it can be other things depending on the speed of cooling). 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. 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.

Quartz is also used in agriculture, paving, brick and tile, concrete, cleansers, foundry casting, paint, glass, soaps, fiber glass, electronics, plaster, sandblasting, industrial effluent filtration, drinking water filtration, hazardous waste control.

Related Information

Substituting alumina in a clay body dramatically lowered thermal expansion

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These are glazed test bars of two fritted white clay bodies fired at cone 03. The difference: The one on the right contains 13% 200 mesh quartz, the one on the left substitutes that for 13% 200 mesh calcined alumina. Quartz has the highest thermal expansion of any traditional ceramic material. As a result the alumina body does not "squeeze" the glaze (put it under some compression). The result is crazing. There is one other big difference: The silica body has 3% porosity at cone 03, the alumina one has 10%!

The same liner glaze crazes on the porcelain but not the stoneware

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The stoneware is made from sedimentary clays mined in a in southwestern Saskatchewan quarry, they have a higher quartz grain content and enough natural feldspar to produce functional density (the practical porosity is about 2.5%). The porcelain on the right is a 45:35:20 kaolin:feldspar:silica blend (there is enough feldspar for about 0.5% porosity). The stoneware has more quartz particles to impose their high thermal expansion because fewer are taken into solution by the feldspar. That means that the body has a whole can put the squeeze on the glaze to prevent it from crazing.

Lazulite Siderite Quartz

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Quartz Rock Rose

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Rutilated quartz

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Cassiterite W Quartz

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Cordierite In Quartz

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Closeup of in-situ quartz mineral at the MGK quarry site in India

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Health warning phrases on a bag of ground silica

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Micro photograph taken by an ordinary iPhone is still very useful

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Micro photo of clay particles

These are 40 mesh particles, about 400 microns in size. They are clearly visible as rounded, not angular. The carbon and high iron mineral particles are easy to spot. The rest appear to be quartz (having various levels of purity from amber to crystal clear). The interesting thing about these is where they come from: A very dirty-looking terra cotta clay. Something else interesting: At 50, 80 and 100 mesh the iPhone, even with its computational photography, was also able to capture the particles - and they looked exactly the same. Their presence explained a number of physical properties of the clay that otherwise seemed odd.

Links

Materials Clay 216
Materials Clay 215
Materials Clay 246
Materials Clay 220
Materials Clay 220
Materials Clay 222
Materials Clay 232
Materials Clay 233
Materials Clay 244
Materials Clay 261
Materials Feldspar 632
Materials Feldspar 635
Materials Feldspar 645
Materials Feldspar 661
Materials Kaolin 111
Materials Kaolin 113
Materials Kaolin 114
Materials Kaolin 115
Materials Kaolin 143
Materials Dolocron 40-13
Materials Primas FA-200 Feldspar
Materials F7 Feldspar
Materials F7/SE Feldspar
Materials F7/SG Feldspar
Materials M74 Feldspar
Materials FM6 Feldspar
Materials KM71 Feldspar
Materials P8 Quartz
Materials P4 Quartz
Materials P30 Quartz
Materials VR4/MQ4 Quartz
Materials VR16 Quartz
Materials FK45 Feldspar
Materials Aplite A/3
Materials Ryolite S1
Materials Newman Red Clay
Materials Prestige AK
Materials B Clay
Materials Silica
Silica, sold as a white powder, is pure quartz mineral. Quartz is pure SiO2 silicon dioxide. It is the most abundant mineral on earth and most used in ceramics.
Materials Crystalline Silica
Materials Pegmatite
Materials Silica Sand
Materials Kaolin 233
URLs http://en.wikipedia.org/wiki/Quartz
Quartz on WikiPedia
URLs http://en.wikipedia.org/wiki/Quartz_inversion
Wikipedia quartz inversion
URLs https://www.ilo.org/global/topics/safety-and-health-at-work/resources-library/publications/WCMS_118100/lang--en/index.htm
Crystalline silica in respirable airborne dusts at International Labour Organization
URLs http://www.handbookofmineralogy.org/pdfs/Quartz.pdf
Quartz mineralogy data
Glossary Mineralogy
Raw ceramic materials are minerals or mixtures of minerals. By taking the characteristics of these into account technicians can rationalize the application of glaze chemistry.
Glossary Cristobalite Inversion
In ceramics, cristobalite is a form (polymorph) of silica. During firing quartz particles in porcelain can convert to cristobalite. This has implications on the thermal expansion of the fired matrix.
Glossary Quartz Inversion
In ceramics, this refers to the sudden volume change in crystalline quartz particles experience as they pass up and down a temperature window centering on 573C.
Glossary Flameware
Flameware is ceramic that can withstand sudden temperature changes without cracking. The low thermal expansion of true flameware makes craze-free glazes very difficult.
Glossary Mineral phase
Oxides SiO2 - Silicon Dioxide, Silica
Oxides Sm2O3 -
Minerals Quartzite
Sandstone metamorphically converted to rock.
Minerals Granite
Granite is a plutonic rock is found throughout the continental crust, most commonly in mountainous a
Hazards Dealing With Dust in Ceramics
A checklist for changes and additions to your tools and equipment and suggestions for habit you need to develop to control dust in your workplace.
Hazards Quartz Toxicity
Typecodes Silica/Quartz
Quartz is very abundant and there are many grades and name brands.
Temperatures Quartz inversion (alpha-beta) (540-600)
By Tony Hansen
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