Plastic fire clay forms a sticky, soft mass when wetted and kneaded with water, and will bond together other clays or rocks. Large plastic fire clay deposits occur in Audrain, Callaway, and St. Louis counties, and lesser quantities are known in Boone, Osage, Gasconade, and Phelps counties. The larger deposits assume a blanket shape with a highly irregular lower surface. Flint Fire Clay Flint fire clay is very fine-grained, smooth or slick, and breaks with a shell-like (conchoidal) fracture. It varies in color from white to black, but most flint fire clay mined is near to white. It is relatively non-plastic—that is, does not readily slake or form a sticky mass when worked a little in water. In fact, flint fire clay has been used locally as road surfacing because it does not become very muddy and sticky. Of course, it is inferior to black-top or concrete road surfaces and has too high a commercial value now to be used extensively as road metal. A hard, white variety of flint fire clay which breaks with numerous conchoidal fractures in appropriate shaped fragments has been called locally “pop-corn flint.” This clay, and other sand-free flint clay, when crushed between one’s teeth “goes to water” in the mouth. Many clay miners use the chewing test to establish the freedom of their clays from gritty sand, which renders flint clay inferior in quality. [Illustration: Flint fire clay showing typical “slick break” and conchoidal fracture, from near New Florence.] Flint fire clays occur geologically in old land depressions and in roughly funnel-shaped pits surrounded by an enclosing layer of sandstone, the whole lying within limestone country rock. The most prominent flint fire clay deposits are found in Callaway, Warren, Lincoln, Osage, Gasconade, Maries, Franklin, and Phelps counties. Diaspore Clay Diaspore clay is a harsh, usually porous, earthy type of clay which has been found in Warren, Osage, Gasconade, Maries, Franklin, Phelps, and Crawford counties in Missouri. Some diaspore clay is mealy, or finely granular, some is chalky to compact, and much of it is more or less oolitic. Oolites (oolitic structure) are small rounded bodies varying in size from about bird shot to BB shot size, and those in diaspore may be solid or hollow. Their hollow structure contributes to the porous condition in diaspore clay. See page 29. It is almost impossible to write a description of diaspore clay which can be used to determine it because the clay has so few individual characteristics. A person familiar with diaspore clay, however, can recognize it at a glance. Probably diaspore clay will not be found outside the counties listed above, and within those counties many persons know the clay from contact with the commercial production of it. [Illustration: Diaspore clay, over 70% alumina, from near Belle.]