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Mineral: Quartz


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

Quartz is a fascinating study in the importance of considering the mineralogy of materials (as opposed 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.

Substituting alumina in a clay body dramatically lowers thermal expansion

Substituting alumina in a clay body dramatically lowers thermal expansion

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, alumina has the lowest. 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

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

The stoneware has a higher silica content and is not vitreous. This means there are more quartz particles to impose their high expansion because fewer are taken into solution by the feldspar.

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

Lazulite Siderite Quartz

Quartz Rock Rose

Quartz Rock Rose

Rutilated quartz

Rutilated quartz

Rutilated quartz

Cassiterite W Quartz

Rutilated quartz

Cordierite In Quartz

Rutilated quartz

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

Out Bound Links

In Bound Links

  • (Materials) Clay 216

    Kil 216

  • (Materials) Clay 215

    Kil 215

  • (Materials) Clay 246
  • (Materials) Clay 220

    Kil 220

  • (Materials) Clay 220

    Kil 220

  • (Materials) Clay 222

    Kil 222

  • (Materials) Clay 232

    Kil 232

  • (Materials) Clay 233

    Kil 233

  • (Materials) Clay 244

    Kil 244

  • (Materials) Clay 261
  • (Materials) Feldspar 632

    Feldspat 632

  • (Materials) Feldspar 635

    Feldspat 635

  • (Materials) Feldspar 645

    Feldspat 645

  • (Materials) Feldspar 661

    Feldspat 661

  • (Materials) Kaolin 111

    Kaolen 111

  • (Materials) Kaolin 113

    Kaolen 113

  • (Materials) Kaolin 114

    Kaolen 114

  • (Materials) Kaolin 115

    Kaolen 115

  • (Materials) Kaolin 143

    Kaolen 143

  • (Materials) Dolocron 40-13 - 325 mesh Dolomite, CaMg(CO3)2
  • (Materials) Primas FA-200 Feldspar
  • (Materials) F7 Feldspar - Soda Feldspar
  • (Materials) F7/SE Feldspar - Soda Feldspar

    Feldspar Soda F7/SE

  • (Materials) F7/SG Feldspar - Soda Feldspar
  • (Materials) M74 Feldspar - Soda Feldspar
  • (Materials) FM6 Feldspar - Sodium Potassium Feldspar
  • (Materials) KM71 Feldspar - Potash Feldspar
  • (Materials) P8 Quartz
  • (Materials) P4 Quartz
  • (Materials) P30 Quartz
  • (Materials) VR4/MQ4 Quartz
  • (Materials) VR16 Quartz
  • (Materials) FK45 Feldspar - Sodium Potassium Feldspar
  • (Materials) Aplite A/3
  • (Materials) Ryolite S1

    Riolite S1

  • (Materials) Newman Red Clay - High temperature red burning low plastic stoneware

    Newman Fireclay, Newman Slip

  • (Materials) Prestige AK - Ball clay

    Prestige Ball Clay

  • (Materials) B Clay - Buff Firing Stoneware Clay

    3B, PR#3 B

  • (Minerals) Quartzite

    Sandstone metamorphically converted to rock.

  • (Minerals - Related) Granite

    Granite is a plutonic rock is found throughout the continental crust, most commonly in mountainous areas (it is the most abundant type of rock). The matrix consists mainly of quartz grains (10-50%), p...

  • (Materials - Mineral equivalent) Quartz - SiO2
  • (Materials - Mineral equivalent) Silica - SiO2 - Quartz, Flint
  • (Glossary) Mineralogy

    In contrast to man-made materials (like frits), ceramic minerals have a highly ordered atomic structure and a specific range of crystalline manifestations. By taking the characteristics of these into account technicians can rationalize the application of glaze chemistry when recipes are mixtures of ...

  • (Materials - Contained) Pegmatite
  • (Oxides - Closest mineral equivalent) SiO2 - Silicon Dioxide, Silica
  • (Glossary) Cristobalite Inversion

    Cristobalite is a crystalline form of silica (SiO2). Silica has the rather amazing ability to exist in different crystalline forms (called polymorphs) each of which has subforms (e.g. alpha, beta). Each form has different physical properties. Quartz in the preferred most stable form, the one found i...

  • (Materials - Mineral equivalent) Silica Sand
  • (Materials - Contained) Kaolin 233
  • (Glossary) Quartz Inversion

    The term "quartz inversion" is used in two ways. Often, people are simply referring to the temperature 573C. More likely they are referring the phenomena that occurs there: The sudden volume change that particles experience as they pass up and down (thus it is called an inversion) through 573C. Actu...

  • (Glossary) Flameware

    Flameware is ceramic that can withstand sudden temperature changes without cracking (i.e. stove top burners). Ovenware is another class of ceramics, it is not as resistant to thermal shock as flameware. There is some confusion among clay buyers and retailers about this. For example Japanese Donabe w...

By Tony Hansen

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