350 Penfield — Chemical Composition of Turquois. 



Clarke's suggestion that turquois contains very finely divided 

 admixtures of iron and copper phosphates .as impurities, and also 

 his formula for the pure mineral {normal turquois of Clarke), 

 Groth* expresses the composition as P0 4 A1 2 (0H) 3 .H 3 2 but 

 suggests, however, that the formula is perhaps P0 4 H[Al.(OH)J. 

 In conclusion it may be stated that it is the author's belief 

 that copper and the small amounts of iron are to be regarded 

 as constituents of turquois, rather than as impurities. In sup- 

 port of this idea the constant occurrence of copper, as shown 

 by all the published analyses, may be cited. Furthermore, 

 fiiiety pulverized turquois is only partially dissolved by boiling 

 in a test tube with hydrochloric acid ; hence, if the material 

 contained copper phosphate as an impurity, it would be 

 expected that the copper phosphate would dissolve readily, 

 leaving the basic aluminium phosphate as a pure white residue, 

 while in tests which have been made the insoluble residues 

 have remained blue, from beginning to end of the experiments. 

 Considering the existence in turquois of the univalent radicals 

 [Al(OH) 9 ]r[Fe(OH a ] and [Cu(OH)], the composition of the 

 mineral, as shown by the published analyses, may be expressed 

 as a derivative of ortho-phosphoric acid, as follows : 



[Al(OH) 2 ,Fe(OH) 2 ,Cu(OH),H] 3 P0 4 . 



The [Al(OH) 2 ] radical always predominates, but is not 

 present in fixed proportion. Some analyses (II, III, and VII) 

 conform closely to the formula [Al(OH) 2 ,Fe(OHL,Cu(OH)] 5 

 HP0 4 . 



Disregarding the iron, the calculated composition of tur- 

 quois for two special cases of isomorphous replacements are 

 given below : 



[Al(OH) 2 



, Cu(OH),H] a 



P0 4 , 



Analysis I, 



[Al(OH)o, 



Cu(OH)] 2 : 



BP0 4 , 



Analysis II, 



Al(OH) 2 : 



Cu(OH):H= 



7:1:6. 



page 346. 



Al(OH) 9 



:Cu(OH) = 



12 



:1. 



page 346. 



PA 



34-64 





34-18 





32-13 







32-86 



A1 2 : 



37-32 





36-47 a 





42-61 







42-64 a 



CuO 



8-28 





8-57 





5-52 







5-27 



H 2 



19-76 





19-38 





19-74 







19-34 









Insol. 0-93 











MnO 0-36 



100-00 99-53 100-00 100'47 



a Include the Fe 2 3 . 



Considering that turquois is not a crystallized mineral, the 

 agreement between theory and the analyses is certainly as 

 close as could be expected. 



* Tabellarische Uebersicht der Mineralien, 1898, p. 97. 



Sheffield Laboratory of Mineralogy and Petrography, 

 Yale University, New Haven, June, 1900. 



