206 Genth and Penjield — Contributions to Mineralogy. 



Insoluble Fe 2 3 4-08 



SiO„ 1-92 



H 2 18-24 



As 2 5 39-65 



SO,.. 1-14 



CuO 1-17 



FeO 33-89 



100-09 



It will be seen that this mineral does not represent a mixture 

 of ferric sulphates and arsenates, like the German varieties. 

 The small quantity of sulphuric acid which is contained in it, 

 is almost exactly required for the cupric oxide present to form 

 chalcanthite ; after deducting this, the quartz, and the insoluble 

 ferric oxide as limonite, the composition is : 



Ratio. Calculated. Pure mineral. 



H 2 0.. 17-64 098 5 7 or 23 17*46 19 40 



As 2 5 39-65 0-172 1 4 38-30 43-11 



Fe 2 3 33-89 212 1-23 5 33-74 37.49 



Impurities 9-00 



100-00 



100-00 



corresponding to : 4(Fe 2 As 2 8 ) . Fe 2 (OH) 6 +20H 2 O. 



7. The so-called Gibbsite from Chester County, Pa., 

 a Phosphate. 



Hermann (Bull. Soc. Imp. Nat., Moscow, No. 4, 1868, 496,) 

 publishes an analysis of a grayish pearly mineral, forming a 

 coating of thin delicate concretionary crusts on limonite from 

 the wavellite locality near "White Horse Station, Chester Co., 

 Pa., giving the following composition : A1 2 3 63 - 84, H 2 33 '45, 

 Si0 2 1-50, P 2 5 0-91 and traces of MgO and Fe 2 3 . 



From some preliminary tests which I have made, it appeared 

 that all the so-called gibbsite from this locality is a phosphate. 

 It forms fine pearly scales and very thin incrustations of pearly 

 scales upon wavellite and limonite. Unfortunately, although 

 very liberally furnished with material by numerous friends, 

 the quantities obtained from about half a dozen different speci- 

 mens, varying from O07 to 0*27 of one gram, gave such dis- 

 cordant results that I could not arrive at a definite conclusion 

 as to its composition. The quantities of the different constit- 

 uents gave, as follows : 



A1„0, 



from 



34-60 



36-28 



37-51 



38-09 



41-25 



42-64 



P.O. 



cc 



27-77 



28-71 



29-13 



32-51 



33-29 



35-88 



H,0 



it 



26-82 



27-77 



28-40 



29-59 



30-29 



30-37 



