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Prosopite
A valid IMA mineral species - grandfathered
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About Prosopite
Formula:
CaAl2F4[(OH)4-xFx]
x = 0.0–1.0
Colour:
Greyish, white, turquois, pale bluish; colourless in transmitted light.
Lustre:
Vitreous, Dull
Hardness:
4½
Specific Gravity:
2.88 - 2.894
Crystal System:
Monoclinic
Name:
From the Greek προσωπείον, a mask, in allusion to the deceptive character of the mineral (as pseudomorphs).
Prosopite can form as an alteration product of topaz in topaz-rich greisens (as in Altenberg, Saxony and Schlaggenwald, Bohemia), and in cryolite-bearing pegmatites, either as a primary mineral or as an alteration product of cryolite.
Unique Identifiers
Mindat ID:
3287
Long-form identifier:
mindat:1:1:3287:8
IMA Classification of Prosopite
Approved, 'Grandfathered' (first described prior to 1959)
IMA Formula:
CaAl2F4(OH)4
Classification of Prosopite
3.CD.10
3 : HALIDES
C : Complex halides
D : Ino-aluminofluorides
3 : HALIDES
C : Complex halides
D : Ino-aluminofluorides
11.6.9.1
11 : HALIDE COMPLEXES
6 : Aluminofluorides - Isolated Octahedra
11 : HALIDE COMPLEXES
6 : Aluminofluorides - Isolated Octahedra
8.6.13
8 : Halides - Fluorides, Chlorides, Bromides and Iodides; also Fluoborates and Fluosilicates
6 : Halides of Al
8 : Halides - Fluorides, Chlorides, Bromides and Iodides; also Fluoborates and Fluosilicates
6 : Halides of Al
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 |
|---|---|---|
| Psp | 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 Prosopite
Vitreous, Dull
Transparency:
Transparent, Translucent
Colour:
Greyish, white, turquois, pale bluish; colourless in transmitted light.
Hardness:
4½ on Mohs scale
Tenacity:
Brittle
Cleavage:
Perfect
On {111}.
On {111}.
Fracture:
Irregular/Uneven, Conchoidal
Density:
2.88 - 2.894 g/cm3 (Measured) 2.898 g/cm3 (Calculated)
Optical Data of Prosopite
Type:
Biaxial (+)
RI values:
nα = 1.501 nβ = 1.503 nγ = 1.51
2V:
Measured: 62° , Calculated: 58°
Max. Birefringence:
δ = 0.009
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:
Moderate (negative)
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:
none
Chemistry of Prosopite
Mindat Formula:
CaAl2F4[(OH)4-xFx]
x = 0.0–1.0
x = 0.0–1.0
Crystallography of Prosopite
Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
B2/b
Setting:
C2/c
Cell Parameters:
a = 6.7103(3) Å, b = 11.1619(5) Å, c = 7.374(3) Å
β = 94.919(2)°
β = 94.919(2)°
Ratio:
a:b:c = 0.601 : 1 : 0.661
Unit Cell V:
550.28 ų (Calculated from Unit Cell)
Morphology:
Crystals somewhat tabular {010}. Massive, granular to powdery.
Comment:
Cell from Hongu et al. (2018). Previously given: 6.68, 11.19, 7.38 Å, 94.93°
Crystal Structure
Load
Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
Unit Cell | Unit Cell Packed
2x2x2 | 3x3x3 | 4x4x4
Show
Big Balls | Small Balls | Just Balls | Spacefill
Polyhedra Off | Si Polyhedra | All Polyhedra
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Big Balls | Small Balls | Just Balls | Spacefill
Polyhedra Off | Si Polyhedra | All Polyhedra
Remove metal-metal sticks
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View
CIF File Best | x | y | z | a | b | c
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Rotation
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Labels
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Data courtesy of the American Mineralogist Crystal Structure Database. Click on an AMCSD ID to view structure
| ID | Species | Reference | Link | Year | Locality | Pressure (GPa) | Temp (K) |
|---|---|---|---|---|---|---|---|
| 0014057 | Prosopite | Pudovkina Z V, Chernitsova N M, Pyatenko Y A (1973) Refinement of the crystalline structure of prosopite, CaAl2F4(OH)4 Journal of Structural Chemistry 14 345-347 | 1973 | 0 | 293 | ||
| 0012448 | Prosopite | Pudovkina Z V, Pyatenko Y A (1970) About the structure of the prosopite, Ca[Al2F4(OH)4], and about some features of the fluoroaluminate crystal chemistry Doklady Akademii Nauk SSSR 190 665-667 | 1970 | 0 | 293 |
CIF Raw Data - click here to close
X-Ray Powder Diffraction
Loading XRD data...
Data courtesy of RRUFF project at University of Arizona, used with permission.
Powder Diffraction Data:
| d-spacing | Intensity |
|---|---|
| 4.35 Å | (10) |
| 3.24 Å | (4) |
| 3.07 Å | (5) |
| 2.13 Å | (6) |
| 1.913 Å | (5) |
| 1.837 Å | (6) |
| 1.813 Å | (6) |
Geological Environment
Paragenetic Mode(s):
| Paragenetic Mode | Earliest Age (Ga) |
|---|---|
| Stage 4b: Highly evolved igneous rocks | >3.0 |
| 34 : Complex granite pegmatites | |
| Stage 7: Great Oxidation Event | <2.4 |
| 47a : [Near-surface hydration of prior minerals] | |
| 47g : [Halogen-bearing surface weathering minerals] |
Geological Setting:
Topaz-bearing greisens, porphyry, and in cryolite pegmatites.
Type Occurrence of Prosopite
Geological Setting of Type Material:
Topaz-bearing greisen.
Associated Minerals at Type Locality:
Other Language Names for Prosopite
Common Associates
Associations Based on Photo Data:
| 34 photos of Prosopite associated with Thomsenolite | NaCa[AlF6] · H2O |
| 20 photos of Prosopite associated with Hydrokenoralstonite | Na0.5(Al,Mg)2(F,OH)6 · H2O |
| 16 photos of Prosopite associated with Fluorite | CaF2 |
| 12 photos of Prosopite associated with Quartz | SiO2 |
| 11 photos of Prosopite associated with Cryolite | Na2NaAlF6 |
| 10 photos of Prosopite associated with Gearksutite | Ca[Al(F,OH)5(H2O)] |
| 9 photos of Prosopite associated with Kaolinite | Al2(Si2O5)(OH)4 |
| 8 photos of Prosopite associated with 'Amazonite' | K(AlSi3O8) |
| 8 photos of Prosopite associated with Elpasolite | K2NaAlF6 |
| 8 photos of Prosopite associated with Azurite | Cu3(CO3)2(OH)2 |
Related Minerals - Strunz-mindat Grouping
| 3.CD.05 | Topsøeite | FeF[F0.5(H2O)0.5]4 · H2O |
| 3.CD.05 | Rosenbergite | AlF[F0.5(H2O)0.5]4 · H2O |
| 3.CD.15 | Jakobssonite | CaAlF5 |
Other Information
Notes:
Decomposed by H2SO4.
Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.
Internet Links for Prosopite
mindat.org URL:
https://www.mindat.org/min-3287.html
Please feel free to link to this page.
Please feel free to link to this page.
Search Engines:
Clara Mine, Oberwolfach, Ortenaukreis, Freiburg Region, Baden-Württemberg, Germany