Occurrence at Hebron, Maine. 217 



ated with quartz, a crystal of which was in one case imbedded 

 in the pollucite, also with psilomelane and with another 

 mineral which proves to be a nearly colorless, brilliant caesium- 

 beryl. The pollucite was in the form of irregular fragments, 

 mostly between J and 10 grams in weight, very similar to 

 those figured by Breithaupt in his original description of the 

 mineral from Elba. The substance of many of the fragments, 

 such as were used for the analysis, was of the most perfect 

 physical character, perfectly colorless and as brilliant and 

 transparent as the finest glass. 



Prof. S. L. Penfield has kindly made the following report 

 of an optical examination of the substance : 



" Refractive indices on a prism of 43°41' : 

 n = 1-5215 Li 

 n = 1*5247 Na 

 n=z 1*5273 Tl 



" The mineral shows no double refraction, hence it is iso- 

 metric. Under the microscope it is very free from inclusions. 

 Some of the specimens show a series of holes, in parallel posi- 

 tion, extending into the substance of the fragment at right- 

 angles to its surface. These holes have rectangular cross- 

 sections and they give to some of the specimens a sort of 

 fibrous structure." Unfortunately, none of the fragments 

 have any distinct crystalline faces. 



In its pyrognostic properties, its luster and hardness and its 

 lack of any apparent cleavage, it agrees exactly with the obser- 

 vations of Breithaupt, Plattner and the other observers in 

 regard to the Elba mineral. It is completely, though slowly, 

 decomposed by hydrochloric acid with the separation of pul- 

 verulent silica. This agrees with the observations of Plattner 

 and Pisani, but not with the statements of Rammelsberg. The 

 latter was doubtless deceived by the slowness of the action, for 

 it takes several hours to decompose the finely pulverized 

 mineral with moderately concentrated acid at the heat of the 

 water-bath. 



The specific gravity of the Hebron mineral was taken twice 

 on each of two fragments; one gave 2*985 and 2*987, the other 

 2*976 and 2*977. It will be noticed that the Maine mineral is 

 considerably heavier than that from Elba. Breithaupt gives 

 2*868, 2-876, 2*880 and 2*892; Pisani gives 2*901; Rammels- 

 berg gives for the material used in his first analysis 2*868, and 

 for the pure material used in his second, 2*885 to 2*896. All 

 of this European material, except that used by Rammelsberg 

 for his first analysis, is described by the various observers as 

 being colorless and transparent. The indications are that the 

 higher specific gravities represent the better material, and 



