HOBBS — MINERALOGY OF WISCONSIN. 



135 



GYPSUM FROM MINERAL POINT. 



The specimen about to be described was presented to 

 the University Mineral Collection by a friend, who obtained 

 it from a local collector at Mineral Point. It was sup- 

 posed to be anglesite by the person who collected it, pos- 

 sibly because it occurs on crystals of galena. The crys- 

 tals referred to are long columnar in habit, colorless, and 

 perfectly transparent. Their greatest length is 10™". 

 and their greatest breadth about 2""". They are attached 

 to small cubes of galena which are covered by a layer of 

 red cryptocrystalline smithsonite. As this is an unusual ap- 

 pearance for the local smithsonite, it was determined to be 

 that mineral by its reacting for zinc on charcoal and being 

 completely soluble with effervescence in hydrochloric acid. 

 The red color of the mineral is superficial, the under por- 

 tions having the usual gray color. 



Fig. 8. — Selenite from Mineral Point. 



The transparent colorless crystals which are attached to 

 the smithsonite and galena, are not anglesite as supposed, 

 but gypsum or selenite. They have the usual habit of 

 gypsum crystals, being bounded by the prism and clino- 

 pinacoid and the rounded terminal planes, I, (111) and occa- 

 sionally e, (103) (see fig. 8). The following measurements 



