Clay minerals originate, in general, from the weathering of previously existing silicate rocks and have therefore been called, on occasions, “rotted rocks.” The writer has long insisted that clays, particularly fire clays, should be thought of instead as purified or refined rocks. The original silicate rocks and minerals, which were rich in constituents melting at low temperatures, have been soaked, leached, and washed by chemically active ground water and rain water until many of the undesirable elements have been carried away, leaving a refined material which we use and know as fire clay. Missouri possesses one of the largest reserves of finest quality fire clay in the world. Special bulletins on Missouri fire clay are published by the State Geologist, Rolla, Missouri, and may be obtained from his office. [Illustration: Plastic fire clay. Shows typical break and naturally polished slicken-sided surfaces. From Mexico, Missouri.] [Illustration: Typical break.] Persons who have undeveloped fire clay deposits on their property frequently ask advice on whom to contact and how to arrange for sale of their fire clay, with the expectation of a fair return and fair treatment. The writer recommends in such cases that the owner of the clay dig into his deposit to obtain a fresh, clean, _representative_ specimen of his fire clay (about one pound) and send it to one or more of the large substantial fire brick or refractories companies operating in Missouri. Obviously the company located nearest the deposit, or with the lowest-cost shipping facilities, will be in a favored position to purchase the clay. If the individual is skeptical about the trustworthiness of the company’s report, he may send opposite parts of the sample lumps to competitive companies. Of course, the individual may have his clay tested by an independent laboratory at his own expense, but this is ordinarily a useless, costly experience because a company will duplicate those tests in its own laboratory before purchasing the clay. If the refractories companies find the clay useful to them they will proceed with negotiations. If the clay is of inferior quality or if it is not needed by the particular company at _that time_, even though of acceptable quality, usually the company will return a truthful report at no cost to the clay owner. The same general advice is given in regard to the development of any mineral deposit which the holder may have. The caution about obtaining a representative sample is especially to be emphasized. It applies to the metallic ores, mineral water, and common rock as well as to fire clay. Plastic Fire Clay