Koenig — New Species Melanochalcite and Keioeencnvite. 405 



This material reminded me of the German "Knpferpecherz," 

 vvhicli has been declared by eminent authorities as a mineral 

 mixture of various bodies — chiefly chrysocolla and limonite. 

 Dana places it under chrysocolla. I have analyzed such 

 material comino^ froai the Old Dominion Mine, Arizona, of a 

 brown-black color. It was more the esthetic beauty of the 

 present material which induced me to enter into its study, 

 than the expectation of finding new facts. Absence of definite 

 crystalline form is ever apt to call up a prejudice against the 

 homogeneity or chemical integrity of bodies. In the present 

 instance, additional reluctance was caused by thinness of the 

 black zone. But since there was plenty of material, the ques- 

 tion of obtaining a snfiicient quantity of satisfactory substance 

 could be answered by care and patience. 



Physical Examination. — I picked out successively, and 

 from different nodules, three portions of material — A, B, C. 

 The sequence of the letters denotes the degree of scrutiny 

 employed. "A" was intended for preliminary work, ''B" 

 for chemical orientation, and '' C " for the final trial. At the 

 beginning the chief care was the rejection of either red or 

 green particles. But it was quickly discerned that among the 

 dark material there was a lustrous and a dull portion ; a banded 

 and a bandless part. High luster and absence of band-structure 

 go together ; dullness and banding are yoked. Sample "A " 

 was tainted somewhat by red, by green and by dull particles. 

 Sample "B" was only contaminated by dull parts ; but "C" 

 was picked over several times, and contained only brilliantly- 

 black material. This was time-consuming. It will be seen, 

 however, from the analyses that the blemishes were rare even 

 in "A" and "B." The black mineral is fairly hard— about 4: 

 but it is exceedingly brittle. The cause of this brittleness 

 lies, probably, in numerous microscopic fissures. As support 

 for this opinion, I mention the long time required for the ceas- 

 ing of air bubbles to rise, when the mineral was placed under 

 water (specific gravity determination). And also the failure to 

 obtain a thin plate by grinding: the plate going to small 

 pieces long before translucence was reached. When the min- 

 eral is ground in a mortar it shows the disagreeable property 

 of "smearing." The fine powder is coffee-brown in color. 

 Some of the finest dust from sample " C," which had stuck to 

 the mortar, was brushed upon a glass slide, imbedded in 

 Canada balsam and examined under the microscope. It proved 

 to be translucent, letting through yellow-brown light, one par- 

 ticle exactly as the other. The mineralogic uniformity and 

 singleness of this material (" C ") is undoubtable. In polar- 

 ized light these dust particles behaved like an amorphous, 

 or isotropic, body. The specific gravity was found to be 



