Kansas Geological Survey, Bulletin 202, pt. 1, originally published in 1971
Originally published in 1971 as part of Kansas Geological Survey Bulletin 201, pt. 1, p. 3-4. This is, in general, the original text as published. The information has not been updated. An Acrobat PDF version of the complete bulletin (7 MB) is also available.
Field and laboratory observations indicate that the efflorescences of magnesium sulfate widely distributed in Kansas are hexahydrite (MgSO4 · 6H2O), not epsomite (MgSO4 · 7H2O). Epsomite occurs only as a transitional phase in the formation of hexahydrite.
Hexahydrite (MgSO4 · 6H2O) that occurs in Kansas from an underground storage area near Atchison was first identified by this author using the X-ray diffraction method (Tien and Waugh, 1970). Another phase of magnesium sulfate, epsomite or epsom salt (MgSO4 · 7H2O), that has long been known to have wide distribution in Kansas (Mudge, 1881) was also found in the underground storage area. Both field and laboratory evidence indicates that hexahydrite is formed by dehydration of epsomite, which is not stable under laboratory conditions (temperature above 20°C, relative humidity below 70 percent), and that reported wide distribution of epsomite in Kansas is questionable.
On a field trip to central and western Kansas in the winter, the author noted that white efRorescences were very common on the surface of the outcrops (Fig. 1). Samples were collected and kept in airtight jars to prevent dehydration and analyzed by the X-ray diffraction method as soon as they were brought into the laboratory. It was found that all the samples collected were hexahydrite. No trace of epsomite was detected. Samples of white effiorescences were also collected from various places in eastern Kansas during the summer. X-ray diffraction data for these samples also indicated that hexahydrite was the only phase of magnesium sulfate present (Fig. 2).
Figure 1--Hexahydrite on the surface of Carlile Shale (Upper Cretaceous), NE sec. 3, T 11 S, R 17 W, Ellis County, Kansas.
Figure 2--X-ray diffraction patterns for hexahydrite from selected outcrops: (A) Carlile Shale (Upper Cretaceous), NE sec. 3, T 11 S, R 17 W, Ellis County, Kansas; (B) Argentine Limestone (Upper Pennsylvanian), NW sec. 9, T 13 S, R 22 E, Johnson County, Kansas; (C) Toronto Limestone (Upper Pennsylvanian), NW sec. 22, T 14 S, R 18 E, Douglas County, Kansas; (Q) quartz reflection.
The origin and the occurrence of epsomite and hexahydrite has been discussed by Tien and Waugh (1970) on the basis of the evidence obtained from the studies of the underground storage area and from the laboratory. Additional observations from the surface of outcrops confirm the conclusion that epsomite occurs only as a transitional phase in the formation of hexahydrite from solutions. The effiorescences of magnesium sulfate so widely distributed in Kansas are hexahydrite, which, therefore, is a common mineral in the State.
Mudge, B. F., 1881, List of minerals found in Kansas: Kansas Acad. Sci. Trans., v. 7, p. 27-29.
Tien, Pei-lin, and Waugh, T. C., 1970, Epsomite and hexahydrite from an underground storage area, Atchison, Kansas; in, Short Papers on Research in 1969, D. E. Zeller, ed.: Kansas Geol. Survey, Bull. 199, pt. 1, p. 3-7.
Kansas Geological Survey, Ubiquity of Hexahydrite in Kansas
Placed on web May 7, 2009; originally published in May 1971.
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