Moorhead Clay

Page 144

At Moorhead several plants have been built to use the thin upper leached and oxidized portion of the silts of the Red River valley.  Only 16 inches of the clay is of good quality, and an admixture of the underlying clay causes too much trouble in drying.  To work so thin a clay a large area is necessary, and most plants strip the few inches of soil from the workable clay and spread it over the shallow pit from which the clay has already been removed.  This allows the continuous use of the soil for farming, except over the few acres that are being actively worked.  The clay slakes in one minute, and its plasticity is low, as it requires 22 per cent of water for molding.  Its tensile strength is well above 100 pounds to the square inch, even when rapidly dried, and its shrinkage is 5 per cent.  As burned at the University of Minnesota it gave the following results:

The clay becomes hard at cone 3, although satisfactory brick can be made at somewhat lower temperatures.  Its fusion temperature was rather higher than that of most of the clays that contain so much lime, and its range of vitrification was nearly 200°.  The plants that have been operated in this neighborhood made soft-mud bricks on a rather small scale.  They are no longer operated.

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