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Mineral: Kaolinite


The most fundamental clay mineral. This mineral is found in nature in its purest form as kaolin. However it makes up at least part of all ceramic clays. The purest deposits are created as it is weathered from rock and deposited, mixed with other products of the weathering process, in layers and lenses in nearby valleys. Thus kaolins (also called China Clays) are whiter and cleaner than other clays because they are mined near the site where they were weathered and altered (rather than being contaminated when transported and sedimented by water). Because kaolin ore is mixed with other rocks and impurities, it has to be separated using various wet and dry processing methods. Kaolin can be found is some sedimentary deposits where it is mixed with quartz and feldspar particles, it can be separated by wet processing methods.

Kaolinite is a pure clay mineral crystal of one part alumina and two parts silica. Most other clay minerals are derivatives of kaolin. Kaolin particles are flat and comparatively the largest of all clay minerals, this makes them among the least plastic. They have a surface chemistry that gives them an affinity for water. The attached water both 'glues' particles together and acts as a 'buffer' to lubricate particle-against-particle movement in the plastic matrix.

In it purest form, kaolin melts at 1770C, thus it is quite refractory. However this temperature drops quickly as impurities increase (like feldspar). Kaolin particles have an inner crystalline structure of alternating flat Al2O3, SiO2 and hydroxyl layers. The Al2O3 and SiO2 bind firmly but the hydroxyl layer does not. This structure accounts for the flat shape of kaolin particles and the way they stack and separate in reacting to physical forces. It also accounts for the affinity for water that the particles have and the difference in charge between the flats and edges. In addition, this structure shapes what happens as heat is applied: the hydroxyl is driven off breaking the bonds between the layers and freeing most of the SiO2 and Al2O3 react on their own. Some of the SiO2 combines to form quartz micro-crystals and some of the Al2O3 forms alumina micro-crystals. Both can dissolve in the feldspar glass. Some of the SiO2 and Al2O3 can remain connected to preserve flat kaolinite particles. Of course the way it which this all plays out is dependent on many factors, especially the firing curve.

Out Bound Links

In Bound Links

  • (Materials) Clay 215

    Kil 215

  • (Materials) Clay 216

    Kil 216

  • (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) EP Kaolin - Plastic White Firing Kaolin

    EPK, Edgar Plastic Kaolin, EPK Kaolin

  • (Materials) Ryolite S1

    Riolite S1

  • (Materials) Prestige AK - Ball clay

    Prestige Ball Clay

  • (Materials) B Clay - Buff Firing Stoneware Clay

    3B, PR#3 B

  • (Materials) Sterling Kaolin
  • (Materials) Topaz Kaolin - No longer available, was made by ECCI
  • (Materials) Super Standard Porcelain - White burning high strength Cornish kaolin

    Super Standard Porcelain Kaolin

  • (Materials) Standard Porcelain Kaolin - A white burning high strength Cornish kaolin

    English Standard Porcelain, Eng Stn Porc, Standard Porcelain China Clay

  • (Materials) Sovereign Kaolin - English Kaolin
  • (Materials) Grolleg Kaolin - Fine White Burning English Kaolin, English China Clay

    Grolleg China Clay

  • (Materials) Treviscoe Kaolin - A white burning high strength Cornish kaolin

    Treviscoe China Clay

  • (Materials) NSC Kaolin
  • (Materials) Remblend Kaolin - Englsih Kaolin
  • (Materials) Kernick Kaolin - English kaolin
  • (Materials) LPC Kaolin

    Ceraclay LPC

  • (Materials) WTD Kaolin

    Ceraclay WTD

  • (Materials) Calcined Topaz Kaolin
  • (Minerals - Related) Allophane

    A clay mineral similar to kaolinite.

  • (Minerals - Related) Dickite

    A clay mineral with the same composition as kaolinite but different crystal structure.

  • (Materials - Parent mineral) Kaolin - Al2O3.2SiO2 or Al2Si2O5(OH)4 - Hydrated alumina silicate, Pure clay mineral

    China Clay

  • (Materials - Contained) Kaolin 233
  • (Glossary) Primary Clay

    Kaolinite is the closest thing we have to pure clay mineral. Clays that have been deposited at or near their site of alteration. They typically are contaminated by rocks and mineral particles that must be removed by processing. The cleanest and lowest iron clays are from this type of deposit. Kaolin...

  • (Minerals - Related) Ball Clay

    Ball clay is the most common type of secondary clay. They are much more plastic than kaolin because the particle size is much smaller. Ball clays are available with a wide range of plasticities (a pro...

By Tony Hansen

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