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Silicified Rock in the Ogallala Formation

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The usefulness of the silicified Ogallala rock is shown by physical test data, chemical analyses, and petrographic descriptions.

Eight samples of Ogallala quartzite and one sample of chert were subjected to standard physical tests and chemical analyses by the United States Engineer Corps. The results of these tests, presented in Table 1, have been furnished to us and supplement the petrographic descriptions given above.

Table 1--Data from standard physical tests and chemical analyses of silicified Ogallala rock from Kansas. (Data furnished by the United States Engineer Office, Kansas City, Missouri)

County Location
(sec., T., R.)
Loss freeze and
thaw, 5 cycles,
Abrasion Sol. in HCl,
Chemical Analysis (percent) Rock Type
Loss on
SiO2 Al2O3 Fe2O3 CaO MgO SO3 Moisture Na2O+
Graham31-7-22W2.382.00.356.815.94.902.2188.093.501.350.691.080.00 1.0199.40Quartzite
Graham34-8-22W2.411.050.272.8114.23.621.5297.  100.04Quartzite
Graham13-8-23W2.372.500.444.548.85.622.0886.983.711.891.081.130.00 1.2099.56Quartzite
Norton15-5-21W2.391.540.113.4511.62.781.1898.000.520.  99.86Quartzite
Phillips4-1-19W2.631.750.004.548.8 2.0087.004.011.591.100.00 1.003.30100.00Quartzite
Phillips7-5-17W2.392.420.404.818.35.22.395.401.330.  99.49Quartzite
Phillips23-5-19W2.391.420.  99.60Quartzite
Rawlins10-4-36W2.213.270.498.544.746.3020.3255.081.070.1122.500.800.00  99.88Chert
Rooks10-6-19W2.392.890.778.  99.42Quartzite

Test data--The apparent specific gravity of the nine samples ranges from 2.21 to 2.63; the lowest observed gravity is that of chert from Rawlins County, and the highest represents quartzite from northwestern Phillips County.

The percentage of absorption ranges from 1.05 to 3.27, the highest absorption being shown by the chert sample. More than half the samples had an absorption of more than 2 percent, which is sometimes the maximum allowable for high grade concrete aggregate. In determining absorption the test procedure was in accord with the A.S.T.M. standard test C-127-90, as modified by the Central Concrete Laboratory of the Corps of Engineers, U.S. Army (War Department, 1942, pp. 49-50). Specimens are prepared by quartering the field sample to a size of approximately 5 kg., rejecting all material passing the 3/8 inch sieve. In the case of homogeneous aggregates all material is retained on the one-inch sieve. After drying to constant weight the sample is immersed in water at 15 to 25 degrees Centigrade, thoroughly agitated to remove dust or other coatings from the particles, and allowed to absorb water for 24 hours. The material is then removed from the water, surface dried, and weighed. The percent absorption is calculated from the weight before and after immersion.

The freezing and thawing tests were made according to the A.S.T.M. standard test procedure C-137-38T, as modified by the Central Concrete Laboratory (War Department, 1942. pp. 69-73). The samples were subjected to 5 cycles of alternate freezing and thawing, and the percentage of loss was computed by subtracting from the original weight of the sample the final weight of all particles which had not broken into three or more pieces during testing. The nine samples showed losses ranging from zero to 0.77 percent, all of which are comparatively low.

Abrasion tests were made in a Deval machine, in which the crushed aggregate is placed in iron cylinders that are rotated on a shaft for 10,000 revolutions at a rate of 30 to 33 r.p.m. This test is designed to simulate resistance to wear under traffic conditions. At completion of the test the material is removed from the cylinders and sieved on a No. 12 (1680-micron) sieve, the part passing the sieve being considered as a measure of the wear. Wear is expressed either as percent of loss of original sample, or as the French coefficient of wear calculated by dividing the weight in grams of the detritus under 0.168 cm. in size, per kilogram of rock used, into 400. The test procedure was according to A.S.T.M. standard method D-289-42T (A.S.T.M.,, 1944, pp. 1369-1371). Of the nine samples tested, only that from one quartzite locality in Graham County has a French coefficient of more than 14, and the chert sample and two of the quartzite samples have coefficients below 8. Five of the samples tested fall within a range of 8 to 13. According to Nash (1918, p. 148), "The best wearing rocks have a percent of wear of 2 or coefficient of 20. If this coefficient of wear is below 8, it is considered as low; from 8 to 13 medium; from 14 to 20 high; and above 20, very high."

Solubility of the quartzite samples in hydrochloric acid is less than 6 percent in all cases, whereas the chert sample shows a solubility of nearly 50 percent. Chemical analyses show the silica content of the quartzite samples to range from 86.98 to 98.00 percent, as contrasted with a silica content of 55.08 percent for the chert sample.

As pointed out by Mielenz (1946), petrographic data may have considerable bearing on the usefulness of a rock for concrete aggregate and other construction purposes. Small amounts of opaline silica in aggregate may cause excessive expansion in high-alkali cement (Blanks, 1943); Hanna (1943) has suggested that opal may be deleterious even in low-alkali cement. Mielenz (1946, p. 315) writes that opal does not generally react if the cement contains less than 0.60 percent total alkalies (Na2O plus K2O, expressed as soda equivalents). Since all the rock described in this report contains sizable quantities of opal, its use as a concrete aggregate in conjunction with high-alkali cement may prove unsatisfactory.

Conclusions--The data presented in this report, supplemented by meager information from local users, indicate that the Ogallala quartzite is far superior to any other deposit in the northwestern part of Kansas and in most cases will probably be suitable for railroad ballast and riprap, and possibly also for a local source of road metal. The unusual coloration and mottled appearance of some deposits should make them desirable for monuments and ornamental stone, and if economical methods of quarrying and finishing are developed, the quartzite may be useful as a durable building stone. The rock is harder than many others used for such purposes, and is closely comparable in resistance and weathering properties to a good grade of granite. Although it has been reported that Ogallala quartzite has been used locally with success as concrete aggregate, it contains a large amount of opal (Mielenz, 1946) and caution should be exercised when it is used in concrete or terrazzo, particularly if it is used in conjunction with high alkali cement, until its suitability for such purposes has been more thoroughly investigated.

Physical test data on Ogallala chert are available for only one sample,, and accordingly conclusions concerning its possible uses are not well founded. Furthermore, it is more variable from one locality to another than the quartzite. It seems to be poorly suited to use as a building or ornamental stone, and less satisfactory than the quartzite for riprap, railroad ballast, and road material.

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Kansas Geological Survey, Geology
Placed on web Aug. 20, 2007; originally published July 1946.
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