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Alpeite
A valid IMA mineral species
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About Alpeite
Formula:
Ca4Mn3+2Al2(Mn3+Mg)(SiO4)2(Si3O10)(V5+O4)(OH)6
Colour:
Brownish red
Lustre:
Vitreous, Silky
Hardness:
5½ - 6
Specific Gravity:
3.374 (Calculated)
Crystal System:
Orthorhombic
Member of:
Name:
Named for the type locality, Monte Alpe mine, Italy.
The Ca(Mn3+2Al2)-Mn3+ analogue of ardennite-(V).
At the type locality it crystallized from V- and Mn-rich hydrothermal fluids in an oxidizing environment.
In the structure of alpeite, Mn3+ is the dominant cation in the M1 site and is the dominant trivalent cation in the M3 site, while in all other members of the ardennite group, Al is the dominant cation in the M1 site and is the dominant trivalent cation in the M3 site.
At the type locality it crystallized from V- and Mn-rich hydrothermal fluids in an oxidizing environment.
In the structure of alpeite, Mn3+ is the dominant cation in the M1 site and is the dominant trivalent cation in the M3 site, while in all other members of the ardennite group, Al is the dominant cation in the M1 site and is the dominant trivalent cation in the M3 site.
Unique Identifiers
Mindat ID:
50779
Long-form identifier:
mindat:1:1:50779:4
Similar Names
| Alipite | (Ni,Mg)3Si4O10(OH)2 · nH2O |
IMA Classification of Alpeite
Approved
Approval year:
2016
First published:
2017
Type description reference:
Classification of Alpeite
9.BJ.40
9 : SILICATES (Germanates)
B : Sorosilicates
J : Sorosilicates with Si3O10, Si4O11, etc. anions; cations in octahedral [6] and greater coordination
9 : SILICATES (Germanates)
B : Sorosilicates
J : Sorosilicates with Si3O10, Si4O11, etc. anions; cations in octahedral [6] and greater coordination
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 |
|---|---|---|
| Apt | 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 Alpeite
Vitreous, Silky
Transparency:
Transparent
Colour:
Brownish red
Streak:
Beige
Hardness:
5½ - 6 on Mohs scale
Tenacity:
Brittle
Cleavage:
Perfect
Perfect cleavage on {1 0 0} and good cleavages on {0 1 0 and {0 0 1}
Perfect cleavage on {1 0 0} and good cleavages on {0 1 0 and {0 0 1}
Parting:
With a curved and stepped fracture
Density:
3.374 g/cm3 (Calculated)
Optical Data of Alpeite
Type:
Biaxial (-)
RI values:
nα = 1.747(3) nβ = 1.785(3) nγ = 1.808(3)
2V:
Measured: 73°
Max. Birefringence:
δ = 0.061
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:
r>v, strong
Pleochroism:
Visible
Comments:
Y>Z>X in shades of reddish brown
Chemistry of Alpeite
Mindat Formula:
Ca4Mn3+2Al2(Mn3+Mg)(SiO4)2(Si3O10)(V5+O4)(OH)6
Element Weights:
Scrava Mine, Statale, Ne, Genoa, Liguria, Italy