Silicified Rock in the Ogallala Formation
by John C. Frye and Ada Swineford
Originally published in 1946 as Kansas Geological Survey Bulletin 64, Part 2. This is, in general, the original text as published in 1946. The information has not been updated.
Abstract
Silicified zones and lentils in the Ogallala formation of Pliocene age provide the most abundant rocks of hard and durable character in the central Great Plains, and are known to occur over a region extending from South Dakota to west-central Texas. The two major rock types are so-called quartzite (sandstone and conglomerate with opaline cement) and chert, which consists of opal, chalcedony, various quantities of calcium carbonate, and scattered sand grains. Silicified rock occurs at many stratigraphic positions within the formation, but the type here referred to as quartzite is restricted to the lower part, below the horizon of prominent volcanic ash deposits. The cementing material of the quartzite is believed to have been derived from the hydration and leaching of volcanic ash during Ogallala time; the source of the silica in the chert is thought to have been largely Pleistocene volcanic ash. Deposition of the opaline silica seems to have occurred by the replacement of calcium carbonate.
Field examination, petrographic studies, chemical analyses, and physical tests indicate that the silicified Ogallala rock has a wide range of possible commercial uses. Several million tons of quartzite are available in northwestern Kansas, the greatest abundance being found in southern Phillips County. Sizable quantities of Ogallala chert are known to occur at many localities in Kansas.
Kansas Geological Survey, Geology
Placed on web Aug. 20, 2007; originally published July 1946.
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