54 CONTRIBUTIONS TO MINERALOGY. [bull. 262. 
formed by the trickling of atmospheric waters over and through rocks 
containing a small percentage of copper. This is not surprising, foil 
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 examined 
consists of small dark-green, roughly mammillary forms, coating the 
rock to a thickness of a few millimeters. Examination by the micro- 
scope fails to reveal any recognizable mineral in the cry ptocrystal line 
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 sub] 
stances 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 tirst 
appears, then brownish nitrous vapors, followed by a sublimate which 
is not very volatile, becomes black on further heating 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 absorption of water. If the water Avhich 
condenses in the upper part of the tube on tirst 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. Yana- 
dium is absent. 
The mixture contains presumably the basic nitrate gerhardtitc 
(H B Cu 4 N 2 12 ) and a chloride which is perhaps atacamite. Spangolite, 
the chloride, can hardl} T be present, for the slight amount of SO s showr 
by test does not seem sufficient to account for the large amount o1< 
chloride. 
The only place from which gerhardtite has previously been identitiec , 
is ;it Jerome mines in the central part of Arizona, associated witl 
cuprite and malachite. It was discovered there by Messrs. II. L. Weill 
and 8. L. Pentield. 
