260 A. F. Rogers — Anhydrite and Associated Minerals. 



salt bed. At the salt mines gypsum occurs in small quantities 

 and probably only as a secondary mineral. The explanation of 

 the association of anhydrite with the salt is based upon the 

 experimental work of Rose and others. When sea-water is 

 evaporated 0aSO 4 .2H a O is the first substance to crystallize out. 

 On further evaporation NaCl forms and with it CaS0 4 . That 

 is, anhydrite instead of gypsum forms from a concentrated solu- 

 tion saturated with NaCl. Later magnesium and potassium 

 chlorids and sulphates are formed. In the Kansas deposits these 

 have been dissolved if ever they were formed. 



The salt and anhydrite occur in the lower Permian. Accord 

 ing to Plate Y of the report on Kansas salt,* the salt-beds are 

 between the Wellington and Marion formations. Not a single 

 fossil was found on the saltmine dumps, and this is not strange 

 when we consider the conditions under which these deposits were 

 formed. From evidence gathered in various places it seems 

 certain that throughout the northern hemisphere an arid climate 

 prevailed in the Permian. The poverty of fossils, the occur- 

 rence of Red-beds, and the presence of extensive beds of gypsum 

 and salt, all point to the fact that Kansas was like the rest of 

 the northern hemisphere during Permian time. Now the occur- 

 rence of anhydrite with the salt is additional evidence that the 

 Kansas Permian is like the Permian (Zechstein) of Germany 

 during which time the salt-deposits of Stassfurt, Leopoldshall, 

 Yienenburg, and Bernburg were formed. At all these localities 

 anhydrite occurs with salt. 



Anhydrite. — The massive anhydrite is a gray or reddish gran- 

 ular rock occurring in thin lenticular layers rarely over four 

 inches thick. It resembles gypsum but is heavier (sp.gr. 2*9) and 

 harder (h. 3-J-). A microscopic examination of the rock shows 

 an aggregate of imperfect sub-angular squares and rectangles, 

 with bright interference colors and parallel extinction. Some 

 of the massive anhydrite gives off water in the closed tube. 

 This points to the presence of gypsum, which is shown in a 

 thin section ( figure 1). The mineral with high relief marked 

 a is anhydrite. The spaces between the anhydrite are filled 

 with gypsum marked g, which has low relief, aggregate struc- 

 ture and low-order interference colors. The gypsum has evi- 

 dently formed from the anhydrite by hydration. Dolomite is 

 also present, marked d. Cleavable and fibrous anhydrite occurs 

 in seams often an inch or more thick. The anhydrite has the 

 typical pseudo-cubic cleavage and one of the cleavages is usually 

 parallel to the plane of the seam. The seams are often fibrous 

 in an oblique direction. The explanation of this is shown in 

 figure 2, which represents a cross-section of a seam. The 

 fibrous structure is due to polysynthetic twinning parallel to an 



^Annual Bulletin of the Mineral Resources for 1898. 



