Cervandonite

Cervandonite
Cervandonite
	Cervandonite is a classic and very sought after mineral from Binntal.
General
Category	Silicate mineral
Formula; (repeating unit)	(Ce,Nd,La)(Fe3+; ,Fe2+; ,Ti,Al); 3O; 2(Si; 2O; 7)(As3+; O; 3)(OH)
Strunz classification	9.BE.09.2
Crystal system	Trigonal
Space group	R3m
Identification
Color	Black
Crystal habit	Aggregates and rosettes of tabular crystals
Cleavage	{001} Indistinct
Fracture	Conchoidal
Tenacity	Brittle
Luster	Adamantine
Streak	Brownish black
Diaphaneity	Translucent to opaque
Specific gravity	4.9 (calculated)
Optical properties	Biaxial
Refractive index	nα = 1.990 nγ = 2.000
Pleochroism	Yellowish, reddish brown to black
References

Cervandonite is a rare arsenosilicate mineral. It has a chemical formula (Ce,Nd,La)(Fe³⁺
,Fe²⁺
,Ti⁴⁺
,Al)
₃SiAs(Si,As)O
₁₃ or (Ce,Nd,La)(Fe³⁺
,Fe²⁺
,Ti,Al)
₃O
₂(Si
₂O
₇)(As³⁺
O
₃)(OH).^[4] It has a monoclinic crustal structure with supercell (Z=6), the crystal structure was established as a trigonal subcell, with space group R3m and a = 6.508(1)Ǻ, c = 18.520(3) Ǻ, V 679.4(2) Ǻ³, and Z=3.^[4] It was first described by Buhler Armbruster in 1988, but it has proven to be problem due to the extreme scarcity of single crystals and its unusual replacement of silicon and arsenic.^[6] Cervandonite is named after the location where it was first described, Pizzo Cervandone (Scherbadung), Italy in the Central Alps.^[2]

^ Mineralienatlas
^ ^a ^b http://rruff.geo.arizona.edu/doclib/hom/cervandonitece.pdf Handbook of Mineralogy
^ http://webmineral.com/data/Cervandonite-(Ce).shtml Webmineral data
^ ^a ^b ^c http://www.mindat.org/min-935.html Mindat.org
^ Demartin, F.; Gramaccioli, C. M.; Graeser, S. (1 April 2008). "THE CRYSTAL STRUCTURE OF CERVANDONITE-(Ce), AN INTERESTING EXAMPLE OF As3+ -> Si DIADOCHY". The Canadian Mineralogist. 46 (2): 423–430. doi:10.3749/canmin.46.2.423.
^ Poirier, G., Ercit, T., Tait, K., Piilonen, P., and Rowe, R. (2009) New mineral names. American Mineralogist 94, 399-408.

[1] Mineralienatlas

[Handbook-2] ttp://rruff.geo.arizona.edu/doclib/hom/cervandonitece.pdf Handbook of Mineralogy

[Webmin-3] ttp://webmineral.com/data/Cervandonite-(Ce).shtml Webmineral data

[Mindat-4] ttp://www.mindat.org/min-935.html Mindat.org

[5] Demartin, F.; Gramaccioli, C. M.; Graeser, S. (1 April 2008). "THE CRYSTAL STRUCTURE OF CERVANDONITE-(Ce), AN INTERESTING EXAMPLE OF As3+ -> Si DIADOCHY". The Canadian Mineralogist. 46 (2): 423–430. doi:10.3749/canmin.46.2.423.

[Poirier-6] Poirier, G., Ercit, T., Tait, K., Piilonen, P., and Rowe, R. (2009) New mineral names. American Mineralogist 94, 399-408.

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