Where it forms, where it's found
- Geological setting
Pegmatites and quartz veins in schist
Highly oxidized, Mn, Al metasediments.
- Type locality
- Ardennite-quartz veins
- Salmchâteau
- Vielsalm
- Luxembourg
- Wallonia
- Belgium
50.2686°, 5.9069°
Safety & handling
Physical
Optical
- Optical type
- Biaxial (+) · 2V measured = 30°
- Refractive index
- 1.74 – 1.78
- Surface relief
- High
- Principal indices
- nα 1.759 · nβ 1.74 – 1.78 · nγ 1.774
- Birefringence
- Older literature reports 0.15-0.20; more recent observations give values ranging from 0.015(1) to 0.0181(2).
- Pleochroism
- Strong
X= dark brownish yellow Y= golden yellow X= pale yellow However, more recent observations indicate only <em>weak</em> pleochroism, in medium brownish-yellow (see comments below).
- Dispersion
- strong (but contradictory data are reported; see comments below)
- Notes
The reported older literature optical data for ardennite-(As) differ markedly from more recent observations (see [https://www.rockptx.com/fkm-351-to-fkm-375/#FKM-372]), and appear to be at least partially incorrect. The missing data and apparent inconsistencies are described in more detail here. In addition to the discrepancy in reported birefringence noted above, older literature reports 2Vz° = 0-70°; more recent observations more specifically give 2Vz° = 30(5)° for material from Salmchâteau, although Bermanec <em>et al.</em>, 2021 report 2Vx° = 49(1)° for material from Nežilovo (hence the latter material would be B(-)). Values for nα and nγ are not reported from the older literature, and so are estimated here for material from Salmchâteau sample FKM-372 from the observed δ and 2V°. The nα and nβ values for Nežilovo material reported by Bermanec <em>et al.</em>, 2021 are implausibly low (nα = 1.537(2) and nβ = 1.579(1)) and appear to be erroneous (and also markedly differ from the analogous values obtained by Barresi <em>et al.</em>, 2007 for an Italian example of the related mineral <m>ardennite-(V)</m>.) Dispersion appears variable, with older literature reporting "strong", and also Bermanec <em>et al.</em>, 2021 reporting "strong" with v > r for the Nežilovo material. But Barresi <em>et al.</em>, 2007 do not observe any notable dispersion in their Italian ardennite-(V), and similarly, the FKM-372 Salmchâteau ardennite-(As) shows only at best very weak dispersion, and when discernible r > v. In contrast to the older literature, all the recent work on both the As-dominant and V-dominant species note only weak pleochroism, in tones of yellow or brownish-yellow.
Crystallography
- Cell parameters
- a = 8.7126(8) Å · b = 18.5124(11) Å · c = 5.8108(8) Å
- Ratio a:b:c
- 1 : 2.125 : 0.667
- Z
- 2
- Morphology
Prismatic, radiating fibrous groups.
- Parting
- On (001)
- Comment
Space Group: Pnmm
Chemical composition
- Impurities
- Ca
- Ti
- Cu
Synonyms
- Ardennit
- Ardennita
- Ardennitt-(As)
- Arsenioardennite
- Dewalquit
- Dewalquita
- Dewalquite
In other languages
- French
- Ardennite- · Ardennite-(As) · Dewalquite
- German
- Ardennit-(As)
- Italian
- Ardennite · Ardennite- · Ardennite-(As)
Classification
9.BJ.40
- 9SilicatesClass
- 9.BSorosilicatesDivision
- 9.BJSorosilicates with Si3O10, Si4O11, etc. anions; cations in octahedral [6] and greater coordinationGroup
- 9.BJ.40Ardennite-(As)Species
58.03.01.01
- 58Sorosilicates Insular, Mixed, Single, and Larger Tetrahedral GroupsClass
- 58.03Insular, Mixed, Single, and Larger Tetrahedral Groups with insular single and triple groups (n=1, 3)Type
- 58.03.01Ardennite groupGroup
- 58.03.01.01Ardennite-(As)Species
17.7.4
- 17Silicates Containing other AnionsClass
- 17.7Silicates with vanadate, arsenate or antimonateGroup
- 17.7.4Ardennite-(As)Species
Group, growth & confusion
Literature, links & citation
- —Detaille, Jean (2023) L'Ardennite-(As) un minéral découvert en Belgique. A.G.A.B. (Association des Géologues Amateurs de Belgique) Minibul Numéro Spécial (November 2023).
- 1872von Lasaulx, A. (1872) Ardennit, ein neues Mineral. Neues Jahrbuch für Mineralogie, Geologie und Paläontologie, 930-934.
- 1872von Lasaulx, A. (1872) Vorläufige Mittheilung über ein neues Mineral. Verhandlungen des Naturhistorischen Vereines der Preussischen Rheinlande und Westphalens: 29: 174.
- 1872von Lasaulx, A. (1872) Über ein neues Mineral aus der Gegend von Ottrez. Sitzungsberichte der niederrheinischen Gesellschaft für Natur- und Heilkunde in Bonn. Verhandlungen des Naturhistorischen Vereines der Preussischen Rheinlande und Westphalens, 29, 189-192.
- 1872Pisani, F. (1872) Sur un nouveau silico-aluminate de manganèse vanadifère, trouvé à Salm-Château, en Belgique. Comptes rendus hebdomadaires de l'Académie des Sciences de Paris: 75: 1542-1544. http://visualiseur.bnf.fr/CadresFenetre?O=NUMM-3032&I=1544&M=pagination
@misc{mineral2026,
author = {Mineral Index editorial board},
title = {Ardennite-(As) — Mineral Index},
year = {2026},
url = {https://mineralindex.org/minerals/ardennite-as-322},
note = {Accessed 2026-05-11}
}