242 Kraus and Hunt — Sulphur and Celestite. 



The formation of hydrogen sulphide in this way is of great 

 importance, for no doubt many of the sulphureted waters 

 encountered in localities where celestite-bearing rocks have 

 been noted are to be referred to the above process. These 

 rocks are quite common in southern Michigan and here we 

 also find many so-called " sulphur " wells. 



The formation of sulphur by the reduction of celestite is 

 analogous to the process which by many is supposed to have 

 played an important role in forming the enormous deposits at 

 Girgenti and vicinity on the Island of Sicily. Here it is, 

 however, assumed that gypsum (CaS0 4 , 2H 2 G) has been 

 reduced to the sulphide and then hydrogen sulphide liberated 

 and subsequently oxidized.* 



B. Crystallography of the Celestite. 



As already shown, in the cracks, crevices, and cavitiesf of 

 the lower strata at this quarry beautiful crystallizations of 

 celestite are to be observed. Since crystals of celestite from this 

 locality had not as yet been measured, a large number were 

 collected with this in view. 



The crystals were for the most part clear and transparent, 

 possessiug a slight bluish tint. The faces were bright and the 

 images, on the whole, very good, so that measurements could 

 be made with very great accuracy. 



Two distinct types of crystals were observed and measured. 

 Figure 1 represents the tabular variety. These crystals were 

 about 10 mm in width and 2 mm thick and showed the following 

 forms: c|001|, m\110], «Z{102], and o{011}. The other, 

 prismatic, type is represented by figure 2. These were about 

 6 mm wide and 4 mm thick and showed the following additional 

 forms : a \ 100 } , I \ 010 \, n \ 120 \ , and z{ 111 } . On the prismatic 

 type the pyramid y{122| was also observed, but the images 

 obtained were rather poor and, hence, the readings somewhat 

 doubtful. On a few crystals the pyramid LjlO'oS'll^, f- P-^, 

 was noted, which up to now has not been observed on celestite. 

 Although the indices are large, the reflections were of such a 

 character that no mistake could have been made in the identity 

 of the form. Also on several crystals a small prism face (110) 

 was recorded. In this case, the readings are not to be consid- 

 ered as accurate as in the case of the pyramid just referred to, 

 but nevertheless this prism, which is also new on celestite, 

 must be considered as present. Although this form had not 

 been noted on celestite before, it has been observed on barite. 



* Brauns, Chemische Mineralogie, 1896, 384 and 389 ; also Kemp, The 

 Mineral Industry, 1893, 585. 



fThis Journal [4], xix, 1905, 290. 



