401 



[Genth. 



Lebanon county, Pa. I am indebted to him and also to Mr. J. Taj-lor 

 Boyd, the General Superintendent of the Cornwall Ore Bank, for about a 

 dozen of t^iese exceedingly rare crystals, which I have found to be spha- 

 lerite. Only two or three distinct crystals were obtained, which were 

 octahedra in hemitrope twins. Most of the crystals are very much dis- 

 torted or imperfect for want of space for their development. 



In color, they are between asparagus-green, brownish-green and light 

 brown. Spec. grav. = 4.033. 



The largest crystals are between 4 and 5™" in size. They occur in cavi- 

 ties of magnetite and are associated with a peculiar variety of prehnite, 

 which sometimes envelops the sphalerite, magnetite, pyrite and crystal- 

 lized chlorite, in small scales, frequently altered into a mineral resembling 

 leidyite, which also envelops the magnetite crystals. There is too little 

 of the latter for further examination. 



The analyses of the sphalerite crystals gave the following results : 



1. '2. 



S = 32.69 33.06 



Zn = 66.47 ^ 



Co = 0.34 > 66.96 



Fe = 0.38 ^ 



100.03 



b. Prehnite. 



This occurs in crystalline incrustations upon magnetite, or as lining the 

 cavities of the same. They consist of minute crystals and groups of crys- 

 tals showing the planes I, 0, and ii, forming frequently small globular, 

 coxcomb and fan-shaped aggregations, colorless, white, yellowish and 

 brownish- white. Sp. gr. = 3.043. The prehnite is the most recent forma- 

 tion, its incrustations covering magnetite, sphalerite, pyrite, chlorite and 

 leidyite. The analysis of a carefully selected specimen gave : 

 SiO, = 42.40 



AI263 . = 30.88 



Fe'^Oa =r 5.54 



CaO = 37.03 



H,,0 = 4.01 



Alkalies and MgO = traces 



99.85 



Vni. Pyrophyllite in Anthracite. 



At the meeting of the American Philosophical Society, of July 18th, 

 1879, I mentioned the very interesting occurrence of pyrophyllite in deli- 

 cately fibrous incrustations from the Buck Mountain seam near Mahanoy 

 City, Schuylkill county, Pa. 



Identical in appearance and association it has latelv been observed by 



