Stibarsen or allemontite is a natural form of

arsenic Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, but ...

antimonide Antimonides (sometimes called stibnides) are compounds of antimony with more electropositive elements. The antimonide ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative b ...

(AsSb) or antimony arsenide (SbAs). The name stibarsen is derived from Latin ''stibium'' (antimony) and arsenic, whereas allemonite refers to the locality Allemont in France where the mineral was discovered.Allemontite
Mindat.org It is found in veins at Allemont, Isère, France;

Valtellina Valtellina or the Valtelline (occasionally spelled as two words in English: Val Telline; rm, Vuclina (); lmo, Valtelina or ; german: Veltlin; it, Valtellina) is a valley in the Lombardy region of northern Italy, bordering Switzerland. Toda ...

, Italy; and the

Comstock Lode The Comstock Lode is a lode of silver ore located under the eastern slope of Mount Davidson, a peak in the Virginia Range in Virginia City, Nevada (then western Utah Territory), which was the first major discovery of silver ore in the United ...

, Nevada; and in a lithium

pegmatite A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic com ...

s at Varuträsk, Sweden. Stibarsen is often mixed with pure arsenic or antimony, 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 Founded in 1958, the International Mineralogical Association (IMA) is an international group of 40 national societies. The goal is to promote the science of mineralogy and to standardize the nomenclature of the 5000 plus known mineral species. Th ...

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 In mathematics, physics and chemistry, a space group is the symmetry group of an object in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of an object that leave it unchan ...

Rm No. 166) is variably described as hexagonal, trigonal and rhombohedral because of the overlap between these terms (see

trigonal crystal system In crystallography, the hexagonal crystal family is one of the six crystal families, which includes two crystal systems (hexagonal and trigonal) and two lattice systems (hexagonal and rhombohedral). While commonly confused, the trigonal crystal ...

). Simulation of the

X-ray diffraction X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...

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

{{reflist Arsenic minerals Trigonal minerals Minerals in space group 166 Native element minerals Antimonide minerals