460 Lindgren and Hillebrand — Minerals from Arizona. 



sublimate like the one above mentioned, followed by a dark 

 olive-brown liquid, which on cooling passed though lighter 

 shades of color and solidified as a bright green ring. In general 

 this behavior is very like that of the mixture under examina- 

 tion from Clifton. 



Gerhardtite (H G Cu 4 N 2 12 ). — The cliffs of granite-porphyry 

 in the deeply eroded Chase Creek Canyon at Metcalf in many 

 places show a conspicuous and extensive bright green coating 

 of some copper mineral, which, no doubt, is formed by the trick- 

 ling of atmospheric waters over and through rocks containing a 

 small percentage of copper. This is not surprising, for porphyry 

 in this vicinity is altered throughout by quartz cementation and 

 disseminated cupriferous pyrite. This " green paint," as it is 

 frequently called, is not soluble in water, and more closely ex- 

 amined consists of small dark green, roughly mammillary forms, 

 coating tbe rock to a thickness of a few millimeters. Exam- 

 ination by the microscope fails to reveal any recognizable min- 

 eral in the cryptocrystalline mass. 



Chemical examination led to the interesting result that the 

 copper minerals present consist of a nitrate and a chloride, 

 neither of which has been found elsewhere in the mines of the 

 district. Detrital grains and some silica seem associated with 

 these compounds. The nitrogen seems difficult to account for 

 in the absence or scarcity of animal substances which might 

 have yielded it. Possibly it is contained in the porphyry. 



The closed-tube reactions of the copper minerals forming the 

 mixture on this specimen are as striking in their way as those of 

 the mixture containing spangolite, described elsewhere. Water 

 first appears, then brownish nitrous vapors, followed by a sub- 

 limate which is not very volatile, becomes black on further heat- 

 ing but on cooling yellow-brown. The glass at the bottom of 

 the tube is often yellow-brown when cold. After some hours 

 the sublimate nearly disappears or becomes greenish from ab- 

 sorption of water. If the water which condenses in the upper 

 part of the tube on first applying heat is driven out by the 

 flame, and the mouth of the tube is held in the flame, this is 

 colored deep green by a volatile copper compound (chloride?). 

 On charcoal the flame is azure blue and at the same time green. 

 Vanadium is absent. 



The mixture contains presumably the basic nitrate gerhardtite 

 and a chloride which is perhaps atacamite. Spangolite, the chlo- 

 ride, can hardly be present, for the slight amount of S0 3 shown 

 by test does not seem sufficient to account for the large 

 amount of chloride. 



The only place from which gerhardtite has previously been 

 identified is at Jerome mines in the central part of Arizona, 

 associated with cuprite and malachite. It was discovered 

 there by Messrs. H. L. Wells and S. L. Penfield. 



