W.T./Schaller — Crystallized Turquoise from Virginia. 39 



Following Penfield's* suggestion as to. the relation of the 

 hydroxyl groups, this formula can be interpreted as : 

 CuOH.6[Al(OH) 2 ].H B .(P0 4 ) 4 . 



I believe that this formula expresses the definite composition 

 of turquoise, and a comparison with other analyses shows that 

 this formula is doubtless the correct one. 



Among the best analyses of turquoise is the one by Pen- 

 fieldf on material from Lincoln County, Nevada. This tur- 

 quoise was " of exceptionally fine quality . . . very fine- 

 grained, of a beautiful robin's-egg blue color, and broke with a 

 smooth fracture. . . . when examined under the micro* 

 scope, the turquoise seemed to be perfectly uniform, showing 

 no evidence of being made up of two substances , . . it 

 acted somewhat on polarized light." Density given as 2*791. 



In the following table are given the analysis of the turquoise 

 from Virginia, Penfield's analysis of turquoise from Lincoln 

 Co., Nevada, and in the third column the composition calcu- 

 lated for the formula proposed : 



Analyses of turquoise. 



Calculated for 

 Virginia Nevada Cu0.3Al 2 3 .2P 2 9 .9H.,0 



P 2 5 _ 34-13 34-18 34*12 



A1 2 3 36-50 35-03 36*84 



Fe 2 3 *21 1-44 



CuO 9-00 8-57 9-57 



H 2 20-12 19-38 19*47 



Insol -_. 0*93 



99*96 99*53 100*00 



The agreement of the three analyses is very close, so that the 

 formula Ou0.3Al 2 3 .2P 2 5 .9H 2 expresses definitely the com- 

 position of this mineral. 



Of the other analyses in which the purity of material is not 

 so definitely known as in the two analyses just cited, there are 

 quoted only those given by Penfield4 



The high alumina may be partly accounted for by the 

 admixture of a little aluminous rock. By considering some of 

 the iron present as ferrous oxide, FeO, isomorphously replacing 

 the CuO, the analyses agree very well with the values calcu- 

 lated for the composition. 



The idea of Penfield's that the composition of the mineral 

 should be expressed as [Al(OH) 2 ,Fe(OH) 2 ,CuOH,H] 1 P0 4 can 

 be more definitely fixed now, as the analysis of crystals of tur- 



*Penfield, S. L., On the Chemical Composition of Turquoise. This 

 Journal (4), vol. x, p. 346, 1900. 



f Loc. cit. JLoc. cit. 



