Stibarsen
Stibarsen is SbAs, an arsenic-group mineral: hardness 3 to 4, density 5.8 to 6.2, tin-white, intergrown with arsenic or antimony. Type locality Varuträsk.
Stibarsen is SbAs, a compound of antimony and arsenic in the arsenic group, with its type locality in the Varuträsk pegmatite, Sweden. It is tin-white to reddish grey, metallic, hardness 3 to 4, measured density 5.8 to 6.2, and typically graphically intergrown with native arsenic or antimony, often reniform or mammillary. Older literature called it allemontite.
In short
- Stibarsen is SbAs, listed on the September 2026 IMA-CNMNC Master List with 1982 s.p. and Sweden. The Handbook of Mineralogy files it in the Arsenic group and names the Varuträsk pegmatite, 15 km northwest of Skellefteå, as the type locality.
- The older name is allemontite. The sheet cites Dana's System of 1944 for stibarsen under “allemontite”, part, and Wretblad's 1941 Varuträsk paper on die allemontite. The IMA list has no allemontite entry. The sheet also lists the Chalanches mine near Allemont, Isère.
- Worked from standard atomic weights, ideal SbAs is 61.91% antimony and 38.09% arsenic. The Varuträsk analysis, Sb 61.5% and As 35.0%, gives an atom ratio of Sb0.52As0.48, close to one to one.
- Its density sits between its two neighbours: arsenic 5.63 to 5.78, stibarsen 5.8 to 6.2, antimony 6.61 to 6.72, all measured, on their Handbook sheets. Because it is typically graphically intergrown with arsenic or antimony, a hand specimen's density is the density of a mixture.
- A regex over the IMA list finds two species whose formulas contain only antimony and arsenic together: stibarsen, SbAs, and paradocrasite, Sb2(Sb,As)2, IMA 1969-011 from Australia.
| Species | Formula | Hardness | Density (meas.) | Density (calc.) | Cleavage | Colour | Streak |
|---|---|---|---|---|---|---|---|
| Arsenic | As | 3.5 | 5.63 to 5.78 | 5.778 | Perfect {0001}, fair {101̅4} | Tin-white, tarnishes dark grey | Tin-white |
| Stibarsen | SbAs | 3 to 4 | 5.8 to 6.2 | 6.44 | Perfect in one direction | Tin-white or reddish grey, tarnishes grey | Grey |
| Antimony | Sb | 3 to 3.5 | 6.61 to 6.72 | 6.697 | Perfect {0001}, distinct {101̅1} | Tin-white | Grey |
What is stibarsen?
An antimony arsenide, SbAs, and one of the arsenic group. The name is built from its composition: STIBium for antimony and ARSENic. The sheet describes it as hexagonal, as indistinct crystals; more commonly reniform or mammillary, to 3 cm; also curved lamellar, fine granular, and adds the feature that governs everything a collector can do with it: typically graphically intergrown with arsenic or antimony in exsolution texture.
It is opaque, tin-white or reddish grey, tarnishing grey, with a grey streak and a metallic lustre that the sheet says may be splendent, but not uncommonly dull. Hardness is 3 to 4 and there is one perfect cleavage. It occurs most commonly in hydrothermal veins, but also in pegmatites, with arsenic, arsenolite, antimony, kermesite, stibnite, stibiconite, cervantite, sphalerite, siderite, calcite and quartz.
The IMA list records 1982 s.p., the year of a special-procedure action, with Sweden as the type country, and the Handbook names the Varuträsk pegmatite as the type locality. For what a type locality does and does not tell you, see what is a type locality.
Is stibarsen the same as allemontite?
Allemontite is the older name, and it covered more than stibarsen. The Handbook's stibarsen sheet cites Palache, Berman and Frondel's Dana's System of Mineralogy (1944) for the species under the heading “allemontite”, part: stibarsen is part of what Dana called allemontite. Its first reference, Wretblad (1941), is titled Die allemontite und das System As–Sb, and the Handbook's antimony sheet still lists allemontite among antimony's associates.
Read with the habit line, the practical meaning is plain. Material labelled allemontite may be stibarsen, or stibarsen intergrown with native arsenic or antimony, and the label alone cannot say which. The name is not on the September 2026 IMA list. Keeping the old name on the label beside the current one is the approach set out in how to label and catalogue a mineral collection.
The sheet lists the Chalanches mine, near Allemont, Isère, among stibarsen's localities. The same mine appears on the erythrite and skutterudite sheets in this site's 176-sheet reference set; see erythrite.
How close is stibarsen to SbAs? A worked calculation
Standard atomic weights, Sb 121.760 and As 74.922, give SbAs a formula mass of 196.682: 61.91% antimony and 38.09% arsenic by mass. The sheet prints 61.90 and 38.10, the same figures rounded the other way.
The Varuträsk analysis reads Sb 61.5%, As 35.0%, with Fe 0.85%, S 0.20%, Bi 0.02% and 2.20% insoluble. Dividing by atomic weight: 61.5 / 121.760 = 0.5051 and 35.0 / 74.922 = 0.4672 mol per 100 g. Normalised, that is Sb0.52As0.48, an Sb:As ratio of 1.08. The type material is close to one to one.
Density is less tidy. The sheet's calculated density is 6.44, but the measured range is 5.8 to 6.2, below it. The sheet gives no reason. What the table shows is that stibarsen's measured range lies between arsenic's 5.63 to 5.78 and antimony's 6.61 to 6.72, so a density test cannot tell a stibarsen from an arsenic-antimony intergrowth. Identification rests on analysis or on X-ray diffraction; the sheet's powder pattern, from Varuträsk material, has its strongest line at 2.92 Å.
Where stibarsen is found
The sheet's localities: the Varuträsk pegmatite, Sweden (type locality); Marienberg, Saxony, and St. Andreasberg, Harz, Germany; the Chalanches mine near Allemont, France; Cavnic and Baia Mare, Romania; Příbram, Czech Republic; Hüttenberg, Carinthia; Valtellina, Italy; the Ophir mine on the Comstock Lode, Nevada; Atlin, Alder Island and the Engineer mine, Tagish Lake, British Columbia, and Bernic Lake, Manitoba; the Moctezuma (Bambolla) mine, Sonora, Mexico; and Broken Hill, New South Wales. A few additional localities are known. No British locality is listed.
Stibarsen is roughly two-fifths arsenic by mass, and its associates include arsenolite, an arsenic oxide. Nothing on this page is health or safety advice. Occupational arsenic exposure is governed in Great Britain by HSE EH40 and the COSHH Regulations 2002; the collection-side context is on toxic minerals in a collection, and personal health questions belong with a clinician.
The rest of this reference section is indexed at the species index. There is no catalogue here and nothing here is offered for sale; the wanted list is the only commercial route.