Clays and Shales of Minnesota
By Frank F. Grout
With Contributions by E. K. Soper
United States Geological Survey, Bulletin 678
Washington, Government Printing Office, 1919
[ACO] Page 132
Springfield.—Just east of Springfield, about 30 miles up Cottonwood River from New Ulm, the A. C. Ochs Brick & Tile Co. has developed a large patch of Cretaceous clays along the Chicago & Northwestern Railway. The clay is 20 feet thick above water level and is known to extend over 20 acres. It is gray and thin bedded and contains both pyrite and limonite in concretionary masses an inch or two thick. Over most of its area it is covered with common gray drift and is somewhat variable in sandiness. The [unfired] clay slakes [quality by which a dry lump of clay tends to absorb water and fall to pieces when immersed] in two minutes, is highly plastic [capable of being molded], and requires 29 per cent of water for molding. Its tensile strength [maximum stress it can withstand before breaking] is 200 pounds to the square inch but is much reduced if rapidly dried. Its shrinkage on drying is about 8 per cent. As tested by the Bureau of Standards a sample selected as especially
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rich plastic shale [hard and generally laminated clay] showed serious auger lamination and much danger of cracking on drying. The clay burns buff and pink at low temperatures and chocolate color when vitrified [through intense heating, the clay particles fuse to a very hard, glass-like state]. The range of vitrification is excellent (400° F.). The porosity [ability to absorb fluids] decreases gradually and is less than 1 per cent for over 100° F. without reaching viscosity [change in form]. Burning tests at the University of Minnesota resulted as follows:
| Cone No. | Color. | Shrinkage. | Absorption. |
| Per cent | Percent | ||
| 010 | Buff | 3 | 16 |
| 07 | Salmon | 4 | 12 |
| 05 | …do | 5 | 10 |
| 03 | …do | 8 | 5 |
| 1 | Brown | 9 | 1 |
| 2 | …do | 10 | 1 |
The bricklets tested were too hard to be scratched with a knife at all these temperatures, but they retained their form perfectly. The clay is available for vitrified brick and tile and probably for roofing tile also, if warping can be prevented in drying. A special die might be successful. For analysis of the clay see page 91 [not shown here].
A. C. Ochs has been operating on this clay for 20 years and has manufactured mostly hollow brick and tile, in eight kilns which, when full, contain about 4,000,000 brick. It is planned to use a steam shovel hereafter in working the bank. Both soft-mud and stiff-mud brick are manufactured, and the strength of the product is excellent.
The Minneapolis building inspector found that three well-burned building tile of 91-inch cross section, with two horizontal holes, has an average compressive strength of 965 pounds to the square inch.
The degree of vitrification easily obtained would indicate that the material is suitable for paving brick, but no attempts are now made to produce pavers. Nearly all the vitrified brick are made hollow, to facilitate drying and to make them lighter in weight and reduce shipping charges. Such hollow brick show a resistance to abrasion which, though not such as a paver requires, is encouraging. If the mechanical troubles involved in drying and burning larger blocks without holes can be overcome, the brick will probably stand a good rattler test.
West of Springfield are other outcrops of Cretaceous shales. A shaft sunk here in exploration for coal many years ago passed through a thick series of shale beds, a few of which contained enough organic matter to produce dark colors but not enough to interfere with their use as clay. The banks of the Cottonwood River and its tributary gulches have exposed similar shale. Mr. Ochs has recently built a tile plant west of Springfield, adding to his work of making brick. All the samples taken required a little more heat for vitrification than
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the clay east of Springfield, and all showed a good range of vitrification, which may be taken as favorable indications. All the clays slake in a few minutes and become highly plastic with about 31 per cent of water. Their tensile strength is 200 pounds to the square inch, and they can be dried much more rapidly than the clay at the brickyard east of Springfield. The shrinkage on drying is 8 per cent. Burning tests resulted as follows:
| Cone No. | Color. | Shrinkage. | Absorption. |
| Per cent | Percent | ||
| 06 | Buff | 1 | 20 |
| 03 | Salmon | 5 | 12 |
| 01 | …do | 7 | 8 |
| 1 | Red | 8 | 6 |
| 3 | …do | 9 | 4 |
| 5 | Brown | 9 | 4 |
| 6 | …do | … | 12 |
The clay is hard after heating to cone 04 (1,958° F.), and reaches a viscosity at about cone 5 (2,246° F.), with a low porosity over a considerable range. The temperature of viscosity is rather low for sewer-pipe clay, but the range of vitrification is excellent. On passing the point of fusion the clay swells and becomes blebby [surface marred by air bubbles]. Analyses of the clay by F. F. Grout are as follows:
Analyses of Cretaceous shales from deposits west of Springfield.
| Chemical analysis. | Mechanical analysis. | ||
| Silica | 63.65 | Fine clay | 25.5 |
| Alumina | 17.27 | Coarse clay | 14.0 |
| Iron oxides | 4.75 | Silt | 58.6 |
| Magnesia | 1.21 | Fine sand | 1.4 |
| Lime | 0.06 | Coarse sand | 0.5 |
| Soda | 0.91 | ||
| Potash | 2.47 | ||
| Ignition | 7.36 | ||
| Moisture | 2.03 | ||
| Titanium oxide | 0.62 | ||
| 100.33 | 100.0 |