440 Koenig — Mohaivkite, StiMo-domeykite, Domeykite, 



a thorough investigation and report. On January 18th I reported 

 to Mr. Smith that the mineral substance which he had sent me 

 was a new mineral species which I would call Mohawkite. Later 

 on I received other material from Mr. Smith in which I identi- 

 fied an antimonial domeykite for which I propose the name 

 Stibio-clomeykite, and also some very peculiar intimate mix- 

 tures of Mohawkite with Whitney ite. It appears that the 

 Stibio-domeykite is the more prevalent of the arsenides, and 

 not the Mohawkite as was thought at the start. The vein has 

 since been traced to the outcrop where it was found to form a 

 ridge owing to the quartz in the gangue. 



1. Mohawkite. 



Physical -properties. — Form is massive ; no crystallization of 

 any sort has been observed. The structure is mostly fine 

 granular, sometimes compact. The color on fresh surface is 

 gray with a faint tinge of yellow. Tarnishes very easily, and 

 ( the tarnish is apt to be ultimately dull purple. A yellow 

 brassy tarnish is brought about by boiling, though in cold 

 water the original color lasts for two days and more. The 

 color is, however, no sure guide for identification. The 

 mineral is very brittle, and owing to the granular structure is 

 not possible to fix the degree of hardness ; it is approximately 

 3*5. Spec. gr. at 21° C. (in boiled water but without correc- 

 tions) = 8*07, mean of three closely agreeing trials and with 

 perfect material, of which there was plenty, — 4.6294 grams 

 were taken. 



Chemical properties. — In closed tube gives no sublimate of 

 arsenic ; only a slight sublimate of As 2 3 , owing to the air in 

 the tube. The siibstance melts in the tube at cherry heat, and 

 colors the glass blue if the heating be kept up for a few 

 minutes (Cobalt). In the open tube the reactions are similar 

 but more pronounced owing to the vigorous oxidation. On 

 charcoal in O. F. copious vapors of As 2 3 , odor of arsenic and 

 ultimately a globule of metallic copper. If a fragment of the 

 mineral be placed in a shallow cavity on charcoal, along side of 

 a borax bead of equal size or somewhat larger, and both fused 

 together in the point of the blue flame, so that the metallic 

 globule be exposed to the air, then the borax bead will 

 assume the pure blue color of cobalt. If this treatment be 

 kept up for sometime and a fresh borax bead be taken every 

 minute, then a brown nickel bead will be obtained- and finally 

 a blue or red copper bead ; thus proving all the metals present 

 except the trace of iron. This test (Plattner's) should be used 

 always in examining metallic arsenides. Thus the mineral 

 contains copper, nickel, cobalt, iron (trace) and arsenic. Boil- 



