Deposits of chert, chert gravel, and ganister also are among the variety of mineral materials found in extreme southern Illinois. Chert consists principally of minutely crystalline particles of quartz. Some chert is popularly called flint. In southern Illinois chert occurs in two principal kinds of deposits, those composed of solid ledges and those consisting of gravel. The term novaculite is used in southern Illinois for those solid deposits that are white, comparatively thick, and free of other interlayered materials. No novaculite is mined at present, but it is said to have been sold in past years for making sodium silicate and silica brick.
The chert gravels of southern Illinois are of three kinds—novaculite gravel, Elco gravel, and “Lafayette” Gravel. The novaculite and Elco gravels consist of fragments of chert plus lesser amounts of fine silica particles and clay. The chert fragments of the novaculite gravel are angular, but the Elco gravel includes both angular and rounded fragments. These gravels are white, yellow, brown, or reddish brown, the novaculite gravel usually being the more highly colored. Deposits in Union and Alexander Counties have been used for road surfacing and other purposes. Deposits of chert gravel also occur in Hardin and Saline Counties, and some stream valleys in southern and western Illinois also contain such gravel.
“Lafayette” Gravel consists principally of brown chert pebbles. Most of the pebbles are rounded and have a smooth, semi-polished surface. The sand and clay occurring with the gravel are brown or dark red. In some places there are deposits of coarse, red quartz sand. The gravel is most abundant in the four southernmost counties of the state, and deposits may be as much as 65 feet thick. It is used principally as a road-surfacing material.
Ganister
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.