Stibarsen
{{Short description|Native element mineral}}
{{Infobox mineral
| name = Stibarsen
| category = Arsenic minerals
| boxwidth =
| boxbgcolor =
| image = Stibarsen-202015.jpg
| imagesize =
| caption = Size: 4.7 × 3.3 × 3.3 cm
| formula = AsSb
| molweight =
| system = Trigonal
| class = Hexagonal scalenohedral ({{overline|3}}m)
H-M symbol: ({{overline|3}} 2/m)
| symmetry = R{{overline|3}}m (No. 166)
Pearson symbol: hR6
| unit cell = a = 4.045, c = 10.961 [Å], Z = 6
| strunz =
| color = White, gray, grayish white, reddish white
| habit = Reniform ("kidney like")
| twinning =
| cleavage = Perfect
| fracture =
| tenacity =
| mohs = 3–4
| luster = Metallic
| refractive =
| opticalprop =
| pleochroism =
| streak = grayish-black
| gravity = 5.8–6.2 (meas.); 6.37 (calc.)
| density =
| melt =
| fusibility =
| diagnostic =
| solubility =
| diaphaneity = Opaque
| other = Non-fluorescent, nonmagnetic
| references = [http://webmineral.com/data/Stibarsen.shtml Stibarsen]. Webmineral[http://www.mindat.org/min-3775.html Stibarsen]. Mindat.org[http://rruff.geo.arizona.edu/doclib/hom/stibarsen.pdf Stibarsen]. Handbook of mineralogy
}}
Stibarsen or allemontite is a natural form of arsenic antimonide (AsSb) or antimony arsenide (SbAs). The name stibarsen is derived from Latin stibium (antimony) and arsenic, whereas allemontite refers to the locality Allemont in France where the mineral was discovered.[http://www.mindat.org/min-132.html Allemontite]. Mindat.org It is found in veins at Allemont, Isère, France; Valtellina, Italy; and the Comstock Lode, United States; and in a lithium pegmatites at Varuträsk, Sweden. Stibarsen is often mixed with pure arsenic or antimony,[http://www.britannica.com/EBchecked/topic/16152/allemontite allemontite]. Encyclopædia Britannica on-line and the original description in 1941 proposed to use stibarsen for AsSb and allemontite for the mixtures.Michael Fleischer "New mineral names" American Mineralogist 26 (1941) 456 Since 1982, the International Mineralogical Association considers stibarsen as the correct mineral name.
Structure
Stibarsen has the same crystal structure as arsenic and antimony, with the intermediate values of the lattice parameters. This structure (space group R{{overline|3}}m No. 166) is variably described as hexagonal, trigonal and rhombohedral because of the overlap between these terms (see trigonal crystal system). Simulation of the X-ray diffraction intensities reveals that the Sb and As atoms form ordered (or partly ordered) sublattices in SbAs. The atoms are arranged in warped graphite-like sheets, which extend normal to the c axis. Weak bonding between the sheets accounts for the relatively low hardness of As, Sb and AsSb.
References
{{commons category|Stibarsen}}
{{commons category|Allemontite}}
{{reflist}}
{{Antimonides}}
Category:Minerals in space group 166