Ganister occurs in the hills of Alexander and Union Counties and is a loosely consolidated, granular material consisting of irregular particles up to about an inch in diameter or of masses of material readily disintegrated into such particles. The particles are composed mainly of fine crystalline quartz. Ganister is white, cream, light yellow, or red and occurs in deposits up to 25 feet or more thick. Relatively small tonnages of the light colored ganister are now used, principally in making refractories, but ganister is said to have been more widely used in that field in the past. It is produced from underground mines. Some red ganister, or ganister like material, mined from open pits has been used for road surfacing. Studies of Southern Illinois Materials Survey geologists have mapped the chert- and silica-bearing formations of Alexander and Union Counties and also many of the various kinds of gravel deposits. Samples have been tested to determine their chemical composition and the size of the particles composing them. Laboratory studies by ceramists indicate that novaculite and novaculite gravel, when suitably processed, can be used for making silica brick, which withstands great heat. Canister and the gravels of southern Illinois offer a variety of raw materials awaiting increased industrial use. Sands of Extreme Southern Illinois In southern Illinois deposits of sand laid down in an arm of the ocean that once extended northward into Illinois from the Gulf of Mexico are found in Alexander, Union, Pulaski, Pope, and Massac Counties. The deposits are commonly a light color—white, cream, yellow, or gray. The grains of the sand are almost all quartz and generally are angular. Some of the sands are of almost powder-like fineness, others are fine or medium grained. Many of the sands contain flakes of white mica, a glistening, silvery-looking mineral often mistaken for silver or platinum. Unlike these metals, however, mica is comparatively light in weight and is not metallic. Also present in some sands are small flakes of the mineral graphite. The southern Illinois sands have not been widely used, but some of them have been employed in making concrete. They also may have possibilities for molding and core sand. As a result of work by Survey geologists, the location and properties of many of the southern Illinois sand deposits are known. CLAY AND SHALE Man has used clay in various ways for many hundreds of years. From it he made, and still makes, bricks to build his dwellings, pottery utensils of many kinds, and other useful products. Everyone knows what clay is, yet it is a substance difficult to define. All clays are earth materials, most of them plastic or sticky when wet but firm when dry. If heated sufficiently (fired) they become hard.