Ardennite-(As)

322

mindat:1:1:322:5

e0604f98-7ebf-4a04-a584-f879b83a2c5a

Approved, 'Grandfathered' (first described prior to 1959)

Renamed by the IMA

1872

Renamed from ardennite to ardennite-(As) in 2007.

9.BJ.40

9 : SILICATES (Germanates)
B : Sorosilicates
J : Sorosilicates with Si₃O₁₀, Si₄O₁₁, etc. anions; cations in octahedral [6] and greater coordination

58.3.1.1

58 : SOROSILICATES Insular, Mixed, Single, and Larger Tetrahedral Groups
3 : Insular, Mixed, Single, and Larger Tetrahedral Groups with insular single and triple groups (n=1, 3)

17.7.4

17 : Silicates Containing other Anions
7 : Silicates with vanadate, arsenate or antimonate

Sub-Adamantine

Opaque

Yellow to Brown

6 - 7 on Mohs scale

Brittle

Perfect
Perfect on {010}, distinct on {110}

On {001}

Irregular/Uneven, Sub-Conchoidal

3.69 - 3.75 g/cm³ (Measured)    3.74 g/cm³ (Calculated)

Biaxial (+)

n_α = 1.759 n_β = 1.740 - 1.780 n_γ = 1.774

Measured: 30°

Older literature reports 0.15-0.20; more recent observations give values ranging from 0.015(1) to 0.0181(2).

δ = 0.015

High

strong (but contradictory data are reported; see comments below)

Strong

X= dark brownish yellow
Y= golden yellow
X= pale yellow

However, more recent observations indicate only weak pleochroism, in medium brownish-yellow (see comments below).

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 2V_z° = 0-70°; more recent observations more specifically give 2V_z° = 30(5)° for material from Salmchâteau, although Bermanec et al., 2021 report 2V_x° = 49(1)° for material from Nežilovo (hence the latter material would be B(-)).

Values for n_α and n_γ 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 n_α and n_β values for Nežilovo material reported by Bermanec et al., 2021 are implausibly low (n_α = 1.537(2) and n_β = 1.579(1)) and appear to be erroneous (and also markedly differ from the analogous values obtained by Barresi et al., 2007 for an Italian example of the related mineral ardennite-(V).)

Dispersion appears variable, with older literature reporting "strong", and also Bermanec et al., 2021 reporting "strong" with v > r for the Nežilovo material. But Barresi et al., 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.

Al, As, H, Mg, Mn, O, Si - search for minerals with similar chemistry

Ti,Cu

Orthorhombic

mmm (2/m 2/m 2/m) - Dipyramidal

a = 8.7126(8) Å, b = 18.5124(11) Å, c = 5.8108(8) Å

a:b:c = 0.471 : 1 : 0.314

937.23 ų (Calculated from Unit Cell)

2

Prismatic, radiating fibrous groups.

Space Group: Pnmm

Highly oxidized, Mn, Al metasediments.

ⓘ Ardennite-quartz-veins, Salmchâteau, Vielsalm, Luxembourg, Wallonia, Belgium

Mineralogical Museum University of Wroclaw, Poland.
Musée de Minéralogie, Ecole des Mines de Paris (originally as 'dewalquite').

Pegmatites and quartz veins in schist

von Lasaulx, A. (1872) Ardennit, ein neues Mineral. Neues Jahrbuch für Mineralogie, Geologie und Paläontologie, 930-934.

No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

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