40 W. T. Schatter — Crystallized Turquoise from Virginia. 



Analyses of turquoise. 



Persia. Russia. California. New Mexico. Clarke 

 Calculated Church Nicolajew Moore , A 



PA- 



34-12 



32-86 



34-42 



33-21 



31-96 



32-86 



28.63 



A1 2 3 . 



36*84 



40-19 



[35-79] 



35-98 



39-53J 



36-88 



37.88 



Fe 2 3 . 



_ _ _ _ 



2-45* 



3-52 



2-99 







2-40 



4-07 



CuO__ 



9-57 



5-27 



7-67 



7*80 



6-30 



7-51 



6-56 



H,0__ 



19-47 



19-34 



18-60 



19-98 



19-80 



19-60 



18-49 



X .... 







0-36f 

 100-47 



100-00 



99-96 



98-87 



•54|| 

 99-79 



4-201 





100-00 



99-83 



D 





2-75 



2-89 



2-86 





2-80 





* Given as FeO. The figures would be in better agreement with values 

 calculated from formula if the iron were considered in the ferrous condition. 



f MnO. % Includes some Fe 2 3 . 



S Insoluble, 1*15 ; CaO, 0-13. || Insoluble, 0-16 ; CaO, 0'38. 



■ff Insoluble. 



quoise shows that the Al(OH) 2 ,OuOH, and H are present in 

 fixed amounts, namely in the ratio of 6 : 1 : 5. Penlield's own 

 analysis agrees very closely with these figures.* 



The crystallographical measurements have shown the appar- 

 ent isomorphism of turquoise and chalcosiderite. The formula 

 given for chalcosiderite is Cu0.3Fe 2 3 .2P 2 0..8H 2 0,which differs 

 in form from that proposed for turquoise by one molecule less of 

 water. From Maskelyne'sf description of the material used for 

 the analysis of chalcosiderite it seems probable that the sample 

 was contaminated by a little andrewsite, limenite and dufrenite. 

 These all contain less waterj than chalcosiderite, so that the 

 value obtained is probably a little low and the true amount of 

 water for pure chalcosiderite is higher than that given. The 

 correct formula for chalcosiderite is then more probably to be 

 written with 9H 2 instead of 811,0. The isomorphous char- 

 acter of this mineral with turquoise is then clearly brought 

 out. 



Turquoise, Cu0.3Al 2 3 .2P 2 5 .9H 2 0. triclinic. 



Chalcosiderite, Cu0.3Fe 2 3 .2P 2 5 .9H 2 0. triclinic. 



Summary. 



In closing, the three main points developed in this paper 

 may be briefly restated : 



(1). Turquoise is triclinic with the crystal form as determined. 



(2). Turquoise has the definite composition Cu0.3Al 2 3 .2P 2 6 . 

 9H 2 0. 



(3). Turquoise and chalcosiderite are isomorphous. 



* Penfield deduced the ratios 7:1:6 from his analysis, but 6 : 1 : 5 is still 

 closer. 



t Maskelyne, N. S., On Andrewsite and Chalkosiderite. Journ. Chem. 

 Soc, vol. xxviii, p. 586, 1875. 



X Andrewsite has 8 - 8 percent, limonite 14'5 percent, and dufrenite 10'5 

 per cent water, while chalcosiderite has 15*00 per cent. 



