The defining characteristic is that the clay contains chips of mica or stone.

Since clays contain a very large amount of trace minerals of all sorts, this most likely contributes to the development of a healthy fetus.

This clay contained unusually large amounts of the element iridium, the clue on which the impact theory for mass extinctions was built.

Some clays naturally contain enough temper that they do not required additional tempers.

The chalk and clay in the area contains a large quantity of flint that often finds its way into older local construction.

All clay contains such minerals, and when pottery is fired, the energy stored in the crystals is released as light.

Common clay contains more impurities than fire clay, and does not have as great a resistance to heat.

Typical clays used in gray cement rawmix may contain 5-15% Fe2O3.

The clay is red-brown to pink and often contains mica inclusions.

This clay contained 5% tar oil, so required less fuel to fire.