Refractory clays consist of natural clay materials, mainly clays of the Kaolinite group, together with fine-grained micas and quartz, and may also contain organic matter and sulfur compounds. Refractory materials are ideal for the construction of ovens, barbecues and fireplaces, which must maintain their resistance and structure at high temperatures. Depending on the operation, these materials must resist thermal shocks, be chemically inert, have low thermal conductivity and a low coefficient of expansion.