St. Cloud Clay

About 3 miles south of St. Cloud, along the west bank of the Mississippi, laminated clays occur over many acres to a depth of over 30 feet, though in much of the adjacent territory they are deeply buried under more recent deposits of sand.  At this particular point a tributary stream, Threemile Creek, has washed the sand off and made enough of the clay accessible to supply a couple of brickyards.  As usual, the clay has irregular pockets and layers of sand, the finer parts of which are called quicksand, and the operations have to be carefully watched or the brick will be altogether too weak.  If proper attention is paid to the mixing of the plastic and sandy parts of the deposits, excellent cream-colored brick can be produced.  If an auger machine is used, it may often be necessary to provide lubrication – probably with water – to prevent “ragging” the corners.  The clay is fairly plastic with 29 per cent of water and shrinks 7 per cent on drying.  Its tensile strength is 100 pounds to the square inch.  Burning tests resulted as follows:

The clay is hard after burning to cone 03 (1,994 F.) and reaches viscosity at cone 4 (2,210 F.).  Each plant has a capacity of over 20,000 brick a day.  At one plant both tile and brick are made and some downdraft kilns have been installed, so that the burning of the tile can be more accurately controlled.

Source:
Clays and Shales of Minnesota
Frank F. Grout with contributions by E. K. Soper
United States Geological Survey
Government Printing Office, Washington, D.C., 1919
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