A. F. Rogers — Anhydrite and Associated Minerals. 261 



oblique face. The twinning is probably secondary, as it appar- 

 ently begins at one side of the seam and gradually causes the 

 mineral to take on a fibrous structure. A few minute pseud- 

 cubic crystals of anhydrite were found in close association with 

 halite. These are doubtless secondary and on account of the 

 halite crystallized as anhydrite instead of as gypsum. 



Gypsum. — Gypsum is present as a subordinate mineral and 

 apparently is always secondary. It occurs in some of the mas- 

 sive anhydrite as an alteration product (figure 1). Also coats 

 seams of cleavable anhydrite but as sharply defined layers 

 (figure 2). On the surface of some of the anhydrite specimens 

 are small gray crystals of gypsum mixed with clay. These 

 have evidently been formed since the material was thrown on 

 the dump-piles. 



Dolomite. — Dolomite occurs in minute crystals disseminated 

 through some of the massive anhydrite ( see d, figure 1 ). In 

 habit the crystals are unusual, the forms being (1011) and (0001) 

 as represented in figure 3. Similar crystals occur in gypsum 

 at Hall in the Tyrol. 



Celestite. — A heavy reddish mineral, occurring in masses of 

 imperfect tabular crystals and also in small fibrous forms in 

 the cleavable anhydrite, proves to be celestite. This intimate 

 connection with anhydrite would perhaps indicate that the 

 celestite is a direct deposition from sea water. 



Quartz. — Quartz occurs in small (2 or 3 mm.) pale reddish 

 crystals imbedded in the massive anhydrite. It has the usual 

 faces (1011), (0111), and (1010) and the habit is like that of the 

 Suttrop, Westphalia crystals. 



Pyrite. — Pyrite is found in minute brown oxidized crystals 

 in the anhydrite. It is coated with a yellow alteration product 

 resembling copiapite. 



Halite. — Halite occurs in clear cubic cleavages up to three 

 or four inches in size. Negative crystals filled with a liquid 

 and moving bubbles are common. A red fibrous halite occurs 

 at Kanopolis. Halite is directly associated with anhydrite and 

 is sometimes embeddded in it. 



Careful search was made for the other Stassfurt minerals 

 but none was found. A reddish fibrous mineral very much 

 resembled polyhalite but proved to be celestite. 



Stanford University, California, 

 December, 1909. 



