ON A NEW VARIETY OF CHRYSOCOLLA FROM CHILE. 



By harry F. KELLER. 

 (Read April 23, 1909.) 



Like other cryptocrystalline or amorphous minerals the hydrated 

 siHcates of copper collectively designated as chrysocoUa vary con- 

 siderably in their chemical composition. They also show very 

 marked differences in color, some of the varieties being deep green, 

 while others exhibit various shades of bluish-green and blue. In 

 many instances the color of the mineral is doubtless modified by the 

 presence of admixtures, such as the oxides of iron, manganese or 

 copper, but we can hardly account for the existence of both the 

 decidedly green and the pure blue modifications without assuming 

 that they are different in composition. Thus in the case of the 

 hydrated carbonates of copper, malachite and azurite, the difference 

 in color is known to be due to a difference in the proportions of 

 chemically combined water. 



Now the analyses of certain green varieties of chrysocolla closely 

 approach the composition CuSiOg + 2H2O, but those of other 

 occurrences, and particularly of the blue varieties, have yielded not 

 only different proportions of silica, oxide of copper and water, but 

 also notable quantities of other constituents, like alumina and phos- 

 phoric acid. Among several Chilean chrysocollas of which speci- 

 mens were presented to me by my brother, Mr. Hermann A. Keller, 

 there is one which appears to me of peculiar interest as its analysis 

 may throw some light on the constitution of the blue varieties of 

 the mineral. It was found at Huiquintipa in the Province of 

 Tarapaoa, and is in the form of turquois-blue, enamel-like crusts, 

 disseminated through a honeycombed silicious matrix. It is brittle 

 with a hardness of 3.5. The powder is of a pale greenish color. 

 When heated in the closed tube, the mineral gives off considerable 

 moisture and blackens, and it is readily decomposed by the mineral 

 acids, without gelatinizing. 



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