Pyrochemical changes in Missouri halloysite

For centuries it has been known that the application of heat to a clay or a clay body produces changes that make it an entirely different substance from the original raw clay. Ever since the earliest civilizations produced crude building brick by baking formed clay bodies in the sun\u27s rays, mankind has been speculating on the nature of the changes that convert soft, friable, plastic clays into hard, strong, non-plastic, rock-like masses. It has been only within the last two decades, however, that progress has been made in the solution of problems dealing with the resultant products in fired clay bodies. The development of the petrographic microscope and the technique for crystal analysis by x-ray methods have supplied impetus to numerous investigations dealing with the chemical reactions involved and the crystalline compounds developed in clays on firing, and these tools, in the hands of competent investigators, have produced some excellent results --Introduction, page 1