Stibarsen Locality: American Eagle; Luona Occurrence, Elk Mountain District, Gunnison County , Colorado , USA ( Locality at mindat.org ) Size: 4.7 x 3.2 x 3.2 cm. This is a rich specimen of stibarsen, with spheroidal nodules and massive seams in ore matrix. Even though the label has somehow been lost since then, we know that this is not a European specimen and so is either from Gunnison Co., Colorado or from Ophir Mine in the Comstock Lode, Nevada. However the Nevada locality has no associations of red minerals listed as occurring there, while several occur in the Colorado locale - and this piece has small red flecks of two different species present on it. So although the locality is given without a confirming label, we think it to be a correct one. Ex. Academy of Natural Sciences Philadelphia Collection. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Stibarsen
Natural arsenic antimonide — also called allemontite for its French type locality at Allemont.
Intro adapted from Wikipedia (CC BY-SA).
Stibarsen is an IMA-recognized mineral species in the sulfide class, with the chemical formula SbAs.
It crystallizes in the hexagonal crystal system (space group R-3m). It is a member of the Arsenic structural group.
Key properties: Mohs hardness 3–4; specific gravity 5.8–6.2; Gray streak; Metallic, may be splendent, but not uncommonly dull. R1 –R2: (400) 64.8–67.8, (420) 65.0–68.0, (440) 65.2–68.2 luster.
IMA symbol Sbr, IMA status: approved, named in 1941.
Most commonly in hydrothermal veins, but also in pegmatites.
It is found associated with Arsenic, arsenolite, antimony, kermesite, stibnite, stibiconite, cervantite, sphalerite, siderite, calcite, quartz.
The name refers to the composition, intermediate between antimony, STIBium, and ARSENic.