Nonclay materials

Clays composed of mixtures of clay minerals having from 20—50% of unsorted fine-grain nonclay materials are most satisfactory. Large amounts of iron, alkaHes, and alkaline earths, either in the clay minerals or as other constituents, cause too much shrinkage and greatiy reduce the vitrification range thus, a clay with a substantial amount of calcareous material is not desirable. Face bricks, which are of superior quaHty, are made from similar materials but it is even more desirable to avoid these detrimental components (see Building materials, survey). 

Clays composed only of clay minerals may have higher water of plasticity values than desired. Consequendy, the presence of substantial amounts of nonclay minerals or the addition of materials that reduce the water of plasticity may improve the working characteristics of a clay. 

The clay minerals can now be discussed in terms of their relationship with the phyllosilicates (sheet silicates). It is important to keep clearly in mind here the difference between clay - the material which is dug out of the ground, and which may be a mixture of different clay minerals, together with various nonclay minerals (such as quartz, pyrite, etc), as well as unaltered rock fragments and incorporated organic material (Grim, 1968) - and the clay minerals themselves, which are crystalline compounds of specified stoichiometry and structure. At this stage, we are only considering the structure of the clay minerals. 

Other traditional ceramics include the abrasive cutting, grinding, and polishing group of materials and refractories, with both clay and nonclay types used for heat insulation. Silicon-oxygen-metal combinations (silicates) are found in the majority of the traditional ceramics. 

In addition to clay, many of these products (in particular the whitewares) also contain some nonplastic ingredients the nonclay minerals include flint, or finely ground quartz, and a flux such as feldspar. The quartz is used primarily as a filler material, being... 

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