288 A. R. CROOK — MOLYBDENITE AT CROWN POINT, WASHINGTON 



capping quartz crystals in quartz geodes. At Salzburg it fills out the 

 cavities between well defined quartz crystals. At Crown Point the mo- 

 lybdenite is always separated from the granite which incloses the quartz 

 vein by a layer of quartz, but the quartz is xenomorphic toward the 

 molybdenite, since the form and striations of molybdenite are always 

 evident in the quartz in which the molybdenite crystal is imbedded. 



Associated Minerals 



As far as the writer is aware, molybdenite is not associated with gold 

 and silver at Crown Point. None of the specimens examined contained 

 either of these metals. The statement of such occurrence made in " Min- 

 eral Resources of the United States," 1901, should probably apply to the 

 Holden mine* a few miles farther down the valley. Some distance from 

 the outcropping of the vein toward the inner part of the tunnel chalco- 

 pyrite appears mixed with the molybdenite. The absence of chalcopy- 

 rite near the outcropping may be due to the fact that it has been oxidized. 

 It is well known that even in museums the iron sulfide is preserved with 

 difficulty in the presence of moist air. Upon the addition of water to 

 the mineral, pyrite or marcasite readily change into melanterite, which is 

 easily dissolved. The chalcopyrite, while more stable, in open air read- 

 ily passes into the sulphate, which can be dissolved, and is washed away 

 without leaving a trace. This is a probable cause of the absence of cop- 

 per ores near the surface. 



Source 



The suggestions as to the source of molybdenite are mainly negative. 

 If we assume, which is more than probable, inasmuch as the element is 

 not now present, that the neighboring rock at no time contained molyb- 

 denite, the source could not have been from lateral secretion. If the 

 neighboring rock did contain the substance, it would be difficult to con- 

 ceive of leaching so thorough as to remove the last trace; hence we are 

 led to conclude that the material must have been born by descending or 

 ascending waters, and I see no facts to suggest a choice of the alterna- 

 tives. 



*Mineral Resources of the United States, 1901, p. 266. 



