410 Koenig — New Sjpecies Melcmochalcite and Keioeenawite. 



2. Keioeenawite. 



Occurrence. — In April 1901, driving the fifth level at the 

 Mohawk Mine, Keweenaw Co., Michigan, southwestward from 

 shaft ]N"o. 1 to shaft No. 2, a narrow cross vein was cut through, 

 carrying domeykite and a reddish-metallic mineral having the 

 color and general appearance of massive niccolite. Superin- 

 tendent Fred A. Smith sent me some of the material. Being 

 very busy at the time, I did not investigate this matter until 

 June, after my vacation had begun. The examination revealed 

 then my wrong, first impression, inasmuch as the substance 

 showed copper, nickel, arsenic in the ratio of 2 : 1. Early in 

 July I visited the mine and informed Superintendent Smith 

 that I proposed the name Keioeenawite for this undoubtedly 

 new mineral species. I went under ground for the purpose of 

 gaining some knowledge of the paragenesis of the arsenides for 

 which this mine has now become famous. The large domey- 

 kite-mohawkite vein crosses the amygdaloid copper-bearing 

 bed near the No. 1 shaft at an angle of nearly 45°. The 

 arsenides in large shining masses sit mostly against the reddish 

 amygdaloid, without the intervention of any selvage. There 

 is little parallelism among the several minerals (the least soluble 

 species forming the bordering fringe), which suggests the notion 

 of the fissure having been filled by crystallization from a stand- 

 ing mother liquor. In the absence of parallelism, the mother 

 liquor must have been in motion. The stoping operations on 

 this vein between the second and third levels tend to show 

 the vein as a system of flat lenses. One of them has been 

 stoped out with a rich yield. I found the new vein to be 

 about 1,300 feet from the large one just described, near shaft 

 No. 2. The vein comes into the level very flat, almost parallel 

 with the strike of the bed. It is thin, with a maximum width 

 of 6 inches. The general character is very like that of the 

 large vein ; to wit, absence of parallelism. Sometimes calcite 

 sits against the amygdaloid, sometimes quartz, or again either 

 domeykite or keweenawite. The conditions under which the 

 filling out of the vein took place must have been alike in both 

 veins. I intended to analyze a large sample of the amygdaloid 

 adjacent to the vein in order to learn whether the arsenic per- 

 vades the rock in minute quantities, to find proof or disproof 

 of a lateral leaching. Thus far I have not done this, though 

 the intention still exists. This is one of the reasons why I kept 

 back the publication of the present notice. 



Physical Projperties. — I have observed the mineral only as a 

 massive, very fine granular aggregate which is very brittle and 

 shows flat conchoidal fracture. Hardness about 4, similar to 

 that of domeykite. The color on the fresh fracture is pale 



