66 KELLER— CHRYSOCOLLA FROM CHILE. 



The analyses yielded : 



Calculated for 

 I. II. CuH2(Si03)j+2HjO 



Per Cent. Per Cent. Per C-ent. 



Specific gravity 2.532 



Si02 46.14 45-89 47-31 



CuO 28.85 28.69 31-39 



AI2O3 58 .47 



FeO 1.38 1.33 



CaO 1.64 1.67 



MgO 83 i.oi 



H2O 20.15 20.32 21.30 



99-54 99.38 100.00 



It was found, as a mean of several closely agreeing determina- 

 tions, that two thirds of the water (13-41 per cent.) escapes below 

 125° C, while the remainder (6.83 per cent.) can be expelled only 

 by protracted ignition at a red heat. There can be no doubt, then, 

 that the latter portion is present in the substance as part of an acid 

 salt, as in dioptase for example. Assuming that the other two 

 thirds of the water is simply " water of crystallization " and, further, 

 that the small amounts of iron, calcium, magnesium, etc., are ad- 

 mixtures, the formula calculated from the above analytical data is 

 CuH2( 5103)2 -{- HoO. This differs from the composition generally 

 assigned to chrysocolla in that it shows the Chilean mineral to be an 

 acid metasilicate of copper. I venture to express the belief that a 

 careful reexamination of other blue chrysocollas may lead to similar 

 results. 



Central High School, 

 Philadelphia. 



