S. L. Penfield — Chalcopyrite from Chester Co., Pa. 207 



From all this it is evident that the only conclusion which 

 can be arrived at' at present is that the White Horse Station 

 " Gibbsite " is a hydrous aluminum phosphate of an unknown 

 constitution. 



8. Atacamite. 



Together with the ferric sulphates mentioned under 1, 2 and 

 3, Prof. Henry A. Ward brought from near Sierra Gorda, 

 Chili, the most beautiful specimens of atacamite, both in per- 

 fect crystals and groups of thin laminated crystals, with cleav- 

 age planes as large as 15xlO mm , and of a deep green color. 

 Prof. Ward kindly presented me with some of these groups 

 for analysis. Sp. gr. = 3'740. The analysis gave : 



Ratio. 



or CuCl 2 30-58 0-228 1 



CuO 55-91 0-630 3 



H 2 13-58 0-754 3 



CI 



16-18 



CuO 



H 2 



73 93 



13-58 



Less O for CI... 



10369 

 . 3-64 



100-05 



This closely agrees with : CuCl 2 . 3Cu(OH), 



Chemical Laboratory, 111 S. 10th street, 

 Philadelphia, May 11th, 1890. 



Art. XXV. — Chalcopyrite crystals from the French Creek 

 Iron Mines, St. Peter, Chester Co., Pa. ; by S. L. Penfield. 



During the past year some very unusual and interesting 

 chalcopyrite crystals have been taken from the French Creek 

 mines which are so unlike any that have thus far been de- 

 scribed that they seem worthy of special notice. The author's 

 attention was first called to them in the fall of 1889, by Mr. 

 James Matters, superintendent of the mines, who has kindly 

 furnished him with a number of interesting crystals, not only 

 of this mineral, but also of pyrite,* as well as with a descrip- 

 tion of their mode of occurrence. The author takes great 

 pleasure in acknowledging his indebtedness to Mr. Matters, and 

 also to Messrs. C. S. Bement and Geo. L. English of Phila- 

 delphia, Pa., for the loan of interesting crystals from their own 

 private collections. 



The crystals which are frequently over one centimeter in 

 diameter are built out in all directions and occur either in cal- 

 cite, from which they can seldom be obtained without being 

 broken, or in a fine fibrous or compact scaly material. The 



* Curiously developed Pyrite crystals: this Journal, III, xxxvii, 209. 



