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Prosopite

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Clara Mine, Rankach valley, Oberwolfach, Wolfach, Black Forest, Baden-Württemberg, Germany
© Stephan Wolfsried

Show Prosopite Photos (24)
Formula:
CaAl
 
2
(F,OH)
 
8
System:MonoclinicColour:Greyish, white; ...
Lustre:Vitreous, DullHardness:4½
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.

Classification of Prosopite

IMA status:Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
Strunz 8th edition ID:3/C.03-10
Nickel-Strunz 10th (pending) edition ID:3.CD.10

3 : HALIDES
C : Complex halides
D : Ino-aluminofluorides
Dana 8th edition ID:11.6.9.1

11 : HALIDE COMPLEXES
6 : Aluminofluorides - Isolated Octahedra
Hey's CIM Ref.:8.6.13

8 : Halides - Fluorides, Chlorides, Bromides and Iodides; also Fluoborates and Fluosilicates
6 : Halides of Al
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Type Occurrence of Prosopite

Type Locality:Tin mine, Altenberg, Erzgebirge, Saxony, Germany
Year of Discovery:1853
Geological Setting of type material:Topaz-bearing greisen.
Associated Minerals at type locality:
SideriteKaoliniteHematiteFluorite

Occurrences of Prosopite

Geological Setting:Topaz-bearing greisens, porphyry, and in cryolite pegmatites.

Physical Properties of Prosopite

Lustre:Vitreous, Dull
Diaphaneity (Transparency):Transparent, Translucent
Colour:Greyish, white; colourless in transmitted light.
Hardness (Mohs):4½
Tenacity:Brittle
Cleavage:Perfect
On {111}.
Fracture:Irregular/Uneven, Conchoidal
Density (measured):2.88 - 2.894 g/cm3
Density (calculated):2.898 g/cm3

Crystallography of Prosopite

Crystal System:Monoclinic
Class (H-M):2/m - Prismatic
Space Group:B2/b {B1 1 2/b} {C2/c} {C1 2/c 1}
Cell Parameters:a = 6.68Å, b = 11.19Å, c = 7.38Å
β = 94.93°
Ratio:a:b:c = 0.597 : 1 : 0.66
Unit Cell Volume:V 549.61 ų (Calculated from Unit Cell)
Morphology:Crystals somewhat tabular {010}. Massive, granular to powdery.
X-Ray Powder Diffraction:
Image Loading

Radiation - Copper Kα
Data Set:
Horizontal Axis: ° to ° Vertical Axis: % Source Data: Filtered Data: Peaks:
Data courtesy of RRUFF project at University of Arizona, used with permission.

Optical Data of Prosopite

Type:Biaxial (+)
RI values: nα = 1.501 nβ = 1.503 nγ = 1.510
2V:Measured: 62° , Calculated: 58°
Maximum Birefringence:δ = 0.009

Chart shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:Low
Dispersion:none

Chemical Properties of Prosopite

Formula:
CaAl
 
2
(F,OH)
 
8
Essential elements:Al, Ca, F
All elements listed in formula:Al, Ca, F, H, O

Relationship of Prosopite to other Species

Common Associates:
QuartzKaoliniteFluoriteApatite
Related Minerals - Nickel-Strunz Grouping):

- +
3.CD.05Rosenbergite
AlF
 
3
·3H
 
2
O
Related Minerals - Hey's Index Grouping:

- +
8.6.1Zharchikhite
AlF(OH)
 
2
8.6.2Chloraluminite
AlCl
 
3
·6H
 
2
O
8.6.3Cadwaladerite
Al(OH)
 
2
Cl·4H
 
2
O
8.6.4Cryolithionite
Na
 
3
Li
 
3
[AlF
 
6
]
 
2
8.6.5Cryolite
Na
 
3
[AlF
 
6
]
8.6.6Chiolite
Na
 
5
Al
 
3
F
 
14
8.6.7Elpasolite
NaK
 
2
[AlF
 
6
]
8.6.8Weberite
Na
 
2
Mg[F|AlF
 
6
]
8.6.9Ralstonite
NaMgAl(F,OH)
 
6
·H
 
2
O
8.6.10Koenenite
Na
 
4
Mg
 
9
Al
 
4
Cl
 
12
(OH)
 
22
8.6.11 Chlor-manasseite
Mg
 
x
Al(OH)
 
2x+2
Cl·(x-0.8)H
 
2
O x about 1.75
8.6.12Gearksutite
Ca[Al(F,OH)
 
5
(H
 
2
O)]
8.6.14Yaroslavite
Ca
 
3
Al
 
2
F
 
10
(OH)
 
2
·H
 
2
O
8.6.15Carlhintzeite
Ca
 
2
[F|AlF
 
6
] · H
 
2
O
8.6.16Colquiriite
CaLi[AlF
 
6
]
8.6.17Thomsenolite
NaCaAlF
 
6
·H
 
2
O
8.6.18Pachnolite
NaCaAlF
 
6
·H
 
2
O
8.6.19Zirklerite
(Fe,Mg,Ca)
 
9
Al
 
4
Cl
 
18
(OH)
 
12
·14H
 
2
O (?)

Other Names for Prosopite

Other Languages:
German:Prosopit
Speckstein (of Charpentier)
Russian:Прозопит
Spanish:Prosopita

Other Information

Other Information:Decomposed by H2SO4.
Health Warning:No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for Prosopite

Reference List:Charpentier (1799) Beob. über die Lagerst. der Erze, Leipzig: 32 (as Speckstein).

Breithaupt (1815) Über die Aechtheit der Kryst., Freiberg: 29.

Scheerer, T. (1853) Ueber Pseudomorphosen, nebst Beiträgen zur Charakteristik einiger Arten derselben.- Poggendorffs Annalen der Physik und Chemie: 90: 315-323 (as Prosopit).

Scheerer, T. (1854) Poggendorffs Annalen der Physik und Chemie: 92: 612 (as Prosopit).

Scheerer, T. (1857) Poggendorffs Annalen der Physik und Chemie: 101: 361 (as Prosopit).

Groth (1883) Zeitschrift für Kristallographie, Mineralogie und Petrographie, Leipzig: 7: 487.

Cross and Hillebrand (1885) USGS Bull. 20: 62.

Dana, E.S. (1892) System of Mineralogy, 6th. Edition, New York: 178.

Hillebrand (1899) American Journal of Science: 7: 54.

Goldschmidt, V. (1920) Atlas der Krystallformen. 9 volumes, atlas, and text: vol. 6: 176.

Larsen, E.S. (1921) The Microscopic Determination of the Nonopaque Minerals, First edition, USGS Bulletin 679: 123.

Palache, C., Berman, H., & Frondel, C. (1951), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana, Yale University 1837-1892, Volume II: Halides, Nitrates, Borates, Carbonates, Sulfates, Phosphates, Arsenates, Tungstates, Molybdates, Etc. John Wiley and Sons, Inc., New York, 7th edition, revised and enlarged: 121-122.

Neues Jahrbuch für Mineralogie, Monatshefte (1986): 7: 329-335.

Internet Links for Prosopite

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  • Raman and XRD data at RRUFF project
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    Localities for Prosopite

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