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U.S. Geological Survey
Bulletin 2209-I

Geology of a Middle Tertiary Clay Deposit in the Patagonia Mountains near Harshaw, Santa Cruz County, Southeastern Arizona

By Brenda B. Houser


photograph of hillslope made of clay
Outcrop of the Harshaw clay showing weathered clay slope developed on pale-red and yellowish-gray massive clay. Larger shrubs are about 1 m high.

A middle Tertiary rhyolite tuff on the northeast side of the Patagonia Mountains in Santa Cruz County, southeastern Arizona contains lenses of calcareous low-swelling montmorillonite clay, as much as 10 to 15 m thick. The presence of the tuff has been known for years, but the clay has not been described previously. The clay lenses, which are virtually silt- and sand-free, were probably formed by diagenetic alteration of fairly clean ash-fall-tuff beds. In preliminary tests, the clay exhibited only about 9 percent shrinkage on drying and about 1 percent shrinkage on firing. Cracking and distortion were minimal in both drying and firing. Further testing needs to be done on the clay to determine its suitability as a specialty clay or as an additive to other clays.

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For questions about the content of this report, contact Brenda Houser

Go to other chapters in USGS Bulletin 2209: Bliss, J.D., Moyle, P.R., and Long, K.R., eds., 2002, Contributions to industrial-minerals research: U.S. Geological Survey Bulletin 2209.

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Maintained by: Michael Diggles
Created: January 6, 2005
Last modified: March 19, 2007 (mfd)