Lindgren and Hillebrand — Minerals from Arizona. 453 



Measured. Calculated. 

 ax, 1120 1341 = 28° 55' 28° 48' 



s s, 0221 2021 = 83 48 84 33 



s'a", 2021 1120 = 48 18 47 43 



By crushing some of the material, imbedded in oil under a 

 cover glass, and examination in convergent polarized light, 

 occasional fragments were found which gave a normal uniaxial 

 interference figure, with numerous rings indicating high bire- 

 fringence. The character of the birefringence was found to 

 be positive. Thus in all of its crystallographic and optical 

 relations the material studied is like typical dioptase from 

 other localities." 



Chrysocolla (CuSi0 3 +«H 2 0). — This mineral occurs very 

 commonly in the oxidized part of the deposits, but does not, 

 except in some cases, constitute an important ore. On the 

 whole, it is more abundant in the deposits in porphyry and 

 granite than in those contained in limestone. The usual 

 bluish green or dirty green colors and conchoidal fracture 

 characterize it. It occurs in seams or coatings at many of the 

 mines : abundantly in the Mammoth mine on contact fissure 

 between porphyry and limestone ; at several prospects on the 

 Stevens group in Chase Creek near Garfield Gulch ; in the 

 Terazas fissure vein in porphyry near Metcalf ; at the Metcalf 

 mines and many of the prospects between that place and 

 Morenci ; at the Modoc open cut, Morenci. Technical analy- 

 ses of chrysocolla ore from Terazas mine by the Arizona Cop- 

 per Company gave 



Si0 2 : 31-65 



CuO _ 34-90 



H 2 _ 26-30 



A1 2 3 _ 3-80 



Undetermined 3-35 



100-00 



Normal chrysocolla should have 34*2 per cent Si0 2 , 45*2 per 

 cent CuO, and 20'5 per cent H 2 0, but the analyses show great 

 divergency, many probably being mixtures. Moreover, what 

 has been called chrysocolla probably includes two mineral 

 species. 



The optical characteristics of chrysocolla seem imperfectly 

 known. Dana states that it is cryptocrystalline, while many 

 other text-books, notably one issued in 1902 by Professor 

 Miers, call it " amorphous." 



In most cases the mineral indeed seems cryptocrystalline 

 with bluish gray colors of interference. But this is by no 

 means universal. 



