Clay Minerals and Properties Questions and Answers

Answer: C

Both are true and the reason resolves the apparent contradiction: attraction between edge and face builds the card-house arrangement that traps water and gives a flocculated slip its high viscosity. Deflocculants work by suppressing exactly this edge-to-face attraction.

Answer: D

The interlayer potassium is not readily exchanged and holds the layers together, so illite swells much less than a smectite. It is a common constituent of ball clays and of many brick clays. Its moderate exchange capacity sits between the other two minerals.

Answer: A

It is the purest and whitest of the common clays and is the basis of porcelain and of fine whiteware. Its comparatively coarse particle size gives it low plasticity, which is why ball clay is usually added alongside it.

Answer: B

Correct answer: remains where the parent rock weathered

A residual clay has not moved: it lies on the granite or other feldspathic rock from which it weathered. Because there has been no sorting it is coarser and less plastic than a transported clay, but it is also purer, since nothing else has been mixed into it - which is why china clay, the classic residual deposit, is the white-firing clay of the industry.

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the mechanism. Moving water carries the finest particles furthest and drops them last, so a sedimentary deposit is finer grained and therefore more plastic. The same transport that sorts the clay also introduces organic matter and iron from the ground it crossed, which is why sedimentary clays are more plastic and darker firing than residual ones.

Answer: D

Residual deposits are coarser and less plastic, since nothing has sorted the particles. Sedimentary clays such as ball clay are finer and considerably more plastic as a direct consequence. Transport is what separates the fine fraction out.

Answer: A

Correct answer: organic matter and iron compounds

Ball clay is a sedimentary deposit, and it carries lignite and other organic matter along with iron compounds picked up during transport and deposition. The organic matter burns away, but the iron remains and colours the fired body cream to buff. It is used in a body with china clay for the plasticity ball clay contributes and china clay lacks.

Answer: B

Correct answer: refractoriness at high temperature

Fireclay is low in fluxes - alkalis, iron, lime - and correspondingly high in alumina, so it softens only at high temperature and is used for refractory brick, kiln furniture and saggars. It is neither white firing nor especially plastic, and no clay is soluble in water; those three options describe china clay, ball clay and nothing at all respectively.

Answer: C

A per cent or two transforms the workability of an otherwise short body, which is why it is used with non-plastic materials. More than that raises the drying shrinkage to a point where cracking becomes difficult to control.

Answer: D

Both are true and the reason gives the limit: the same property that makes it so effective a plasticiser also makes it dangerous in quantity, so the addition is kept as small as will do the job. The optimum is found by trial on the particular body.