Lindgren and Hillebrand — Minerals from Arizona. 451 



that a vast number of mineral manganites should exist, and it 

 ought rather to excite surprise than otherwise if two or more 

 are not formed simultaneously from the same solution. This, 

 together with inherent difficulties of analysis, would offer a 

 simple explanation of the fact that so few of the analyses made 

 lead to rational formulas. If formed from solution their original 

 state might well be one of hydration either as regards water of 

 crystallization or of constitution. The temperature at which 

 the water is expelled in the present case indicates constitutional 

 water. 



Our search of the literature has not revealed a native man- 

 ganite carrying a high percentage of lead, although artificial 

 compounds have been prepared. For this reason, and because 

 of its distinctly crystalline character, the present mineral seems 

 worthy of receiving a specific name. The one we propose is 

 Coronadite, after the famous explorer of that portion of the 

 American continent from which the Territories of New 

 Mexico and Arizona have been formed. 



Chalcocite (Cu 2 S). — The cuprous sulphide is very common 

 in the Clifton district, in fact constituting at present the prin- 

 cipal valuable mineral in the ores. It occurs chiefly inter- 

 grown with pyrite, in the altered porphyry as disseminated 

 grains or as solid seams or veins which rarely exceed two or 

 three feet in thickness. It is never crystallized but has ordi- 

 narily an earthy or sooty appearance and black color; scratch- 

 ing it with a knife reveals the semi-sectile character and 

 metallic luster. In a few small massive veinlets the normal 

 metallic luster and dark gray color appear on fractures ; a 

 fibrous or columnar structure of the mineral is known on small 

 seams in shale from the Montezuma mine. The mineral pre- 

 fers porphyry, and the great bodies of ore now worked all 

 occur in this rock ; but it is not entirely unknown from the 

 irregular deposits in limestone generally carrying cuprite and 

 copper carbonates. A partial analysis of massive chalcocite 

 from the Montezuma mine, Morenci, gave 96 per cent Cu 2 S and 

 2*4 per cent FeS 2 , the latter probably mechanically admixed. 



The chalcocite is everywhere, in this district, a secondary 

 mineral formed by the replacement of pyrite by means of 

 descending solutions of cupric sulphate. The deposition of 

 the mineral was accompanied by the formation of quartz, chal- 

 cedony, and kaolin. In the porphyry the chalcocite ore along 

 the veins begins 100 to 200 feet below the surface and con- 

 tinues to a depth of 400 feet, or even more, when it is usually 

 replaced by pyrite, chalcopyrite, and zincblende. 



Silicates. 



Willemite (Zn 2 Si0 4 ). — This rare silicate of zinc was found 



by Mr. Boutwell as very small greyish crystals on a fragment 



Am. Jour. Sci. — Fourth Series, Yol. XVIII, No. 108.— December, ]904. 

 31 



