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Villyaellenite
A valid IMA mineral species
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About Villyaellenite
Villy Aellen
Formula:
(Mn,Ca)Mn2Ca2(AsO3OH)2(AsO4)2 · 4H2O
Colour:
Colorless, orange to light pink
Lustre:
Sub-Vitreous, Resinous
Hardness:
4
Specific Gravity:
3.20
Crystal System:
Monoclinic
Member of:
Name:
Named by H. Sarp in 1984 after Villy Aellen, (1926, Neuchâtel, Switzerland - 2000), zoologist and former Director of the Natural History Museum of Geneva (Switzerland).
Isostructural with:
Compare giftgrubeite, the ordered (Ca:Mn = 3:2) intermediate member between villyaellenite and sainfeldite.
See also the closely related miguelromeroite. Note: The miguelromeroite samples from the Veta Negra mine, Chile, were originally labeled "villyaellenite".
See also the closely related miguelromeroite. Note: The miguelromeroite samples from the Veta Negra mine, Chile, were originally labeled "villyaellenite".
Unique Identifiers
Mindat ID:
4182
Long-form identifier:
mindat:1:1:4182:5
IMA Classification of Villyaellenite
Approved
IMA Formula:
(Mn2+,Ca)Mn2+2Ca2(As5+O4)2(As5+O3OH)2·4H2O
Approval year:
1983
First published:
1984
Classification of Villyaellenite
8.CB.10
8 : PHOSPHATES, ARSENATES, VANADATES
C : Phosphates without additional anions, with H2O
B : With only medium-sized cations, RO4:H2O = 1:1
8 : PHOSPHATES, ARSENATES, VANADATES
C : Phosphates without additional anions, with H2O
B : With only medium-sized cations, RO4:H2O = 1:1
39.2.1.3
39 : HYDRATED ACID PHOSPHATES,ARSENATES AND VANADATES
2 : (AB)5[HXO4]2[XO4]2.xH2O
39 : HYDRATED ACID PHOSPHATES,ARSENATES AND VANADATES
2 : (AB)5[HXO4]2[XO4]2.xH2O
20.8.20
20 : Arsenates (also arsenates with phosphate, but without other anions)
8 : Arsenates of Mn
20 : Arsenates (also arsenates with phosphate, but without other anions)
8 : Arsenates of Mn
Mineral Symbols
As of 2021 there are now IMA–CNMNC approved mineral symbols (abbreviations) for each mineral species, useful for tables and diagrams.
| Symbol | Source | Reference for Standard |
|---|---|---|
| Vy | IMA–CNMNC | Warr, L.N. (2021). IMA–CNMNC approved mineral symbols. Mineralogical Magazine, 85(3), 291-320. doi:10.1180/mgm.2021.43 |
Physical Properties of Villyaellenite
Sub-Vitreous, Resinous
Transparency:
Transparent, Translucent
Colour:
Colorless, orange to light pink
Streak:
White
Hardness:
4 on Mohs scale
Tenacity:
Brittle
Cleavage:
Distinct/Good
{100} good
{100} good
Density:
3.20 g/cm3 (Measured) 3.24 g/cm3 (Calculated)
Comment:
D as high as 3.72, Am Min (1988): 73:1172
Optical Data of Villyaellenite
Type:
Biaxial (-)
RI values:
nα = 1.660 - 1.713 nβ = 1.670 - 1.723 nγ = 1.676 - 1.729
2V:
Measured: 70.5° to 76°, Calculated: 75° to 75.6°
Birefringence:
0.016
Max. Birefringence:
δ = 0.016
Based on recorded range of RI values above.
Based on recorded range of RI values above.
Interference Colours:
The colours simulate birefringence patterns seen in thin section under crossed polars. They do not take into account mineral colouration or opacity.
Michel-Levy Bar The default colours simulate the birefringence range for a 30 µm thin-section thickness. Adjust the slider to simulate a different thickness.
Grain Simulation You can rotate the grain simulation to show how this range might look as you rotated a sample under crossed polars. Each grain retains its interference colour (retardation) while its brightness falls to black at extinction and reaches a maximum between extinction positions.
The colours simulate birefringence patterns seen in thin section under crossed polars. They do not take into account mineral colouration or opacity.
Michel-Levy Bar The default colours simulate the birefringence range for a 30 µm thin-section thickness. Adjust the slider to simulate a different thickness.
Grain Simulation You can rotate the grain simulation to show how this range might look as you rotated a sample under crossed polars. Each grain retains its interference colour (retardation) while its brightness falls to black at extinction and reaches a maximum between extinction positions.
Surface Relief:
Very High (positive)
Relative to Canada balsam mounting medium (n ≈ 1.537).
Relative to Canada balsam mounting medium (n ≈ 1.537).
This shows the grain boundary and Becke line effect under plane-polarised
light, based on the contrast between this mineral's average refractive
index and the mounting medium. It does not take into account mineral
colouration.
In focus
Interference Figure:
This shows the idealized biaxial acute bisectrix (Bxa) interference figure
- the conoscopic view for a grain cut perpendicular to the acute bisectrix, using
this mineral's 2V. The two small white dots mark the melatopes - the points
where the two optic axes emerge - and are shown only when they fall within the
field of view. The coloured bands are isochromatics, and the dark bands are
isogyres.
Rotate the stage: at 0°/90° the isogyres form a cross through the melatopes; at 45° they pull apart into curved hyperbolas. That splitting on rotation - absent in a uniaxial figure - is the standard diagnostic test for telling biaxial minerals from uniaxial ones. If 2V is large, the melatopes may fall outside the field of view, as they often do at the microscope too.
Rotate the stage: at 0°/90° the isogyres form a cross through the melatopes; at 45° they pull apart into curved hyperbolas. That splitting on rotation - absent in a uniaxial figure - is the standard diagnostic test for telling biaxial minerals from uniaxial ones. If 2V is large, the melatopes may fall outside the field of view, as they often do at the microscope too.
Dispersion:
weak
Optical Extinction:
Y ^ c = 30°-40°.
Pleochroism:
Visible
Comments:
X=very pale orange pink, Y=exceedingly pale pink, Z=pale orange pink; Z>>X>Y.
Comments:
Higher optics may represent closeness to end-member.
Chemistry of Villyaellenite
Mindat Formula:
(Mn,Ca)Mn2Ca2(AsO3OH)2(AsO4)2 · 4H2O
Element Weights:
Common Impurities:
Zn,Ca,Fe
Crystallography of Villyaellenite
Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
B2/b
Setting:
C2/c
Cell Parameters:
a = 18.55 Å, b = 9.50 Å, c = 9.99 Å
β = 96.94°
β = 96.94°
Ratio:
a:b:c = 1.953 : 1 : 1.052
Unit Cell V:
1,747.59 ų (Calculated from Unit Cell)
Z:
4
Morphology:
Rosettes of prismatic crystals, elongated || [001], tabular || {100}.
X-Ray Powder Diffraction
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 8.21 Å | (50) |
| 4.45 Å | (30) |
| 3.24 Å | (50) |
| 3.21 Å | (100) |
| 3.13 Å | (30) |
| 3.06 Å | (70) |
| 2.98 Å | (40) |
| 2.34 Å | (30) |
Comments:
ICDD 41-1455, also 37-444.
Săcărâmb, Certeju de Sus, Hunedoara County, Romania