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Cassagnaite, a new, V-bearing silicate mineral from the Cassagna Mine, Northern Apennines, Italy

Riccardo Basso, Cristina Carbone and Andrea Palenzona
Cassagnaite, a new, V-bearing silicate mineral from the Cassagna Mine, Northern Apennines, Italy
European Journal of Mineralogy (February 2008) 20 (1): 95-100


Cassagnaite occurs at the Cassagna manganese mine (Eastern Liguria, Italy), filling fractures in braunite+quartz layered mineralizations together with piemontite. It occurs as very rare isolated prismatic to tabular {001} crystals, usually elongated along [100], and as entangled aggregates of a few crystals. Few aggregates consist of very small cassagnaite crystals (maximum size up to 0.05 mm) closely associated with much larger piemontite, quartz, and braunite crystals. The crystals are generally very small, with a maximum size up to 0.1 mm, golden brown in colour, transparent with vitreous lustre. The crystal structure, refined in the space group Cmcm with cell parameters a = 6.066(1) Aa, b = 8.908(1) Aa, c = 18.995(2) Aa and Z = 2, may be described as a layer stacking along [001] of a fundamental building block of composition [M1 (sub 2) (OH) (sub 2) (SiO (sub 4) ) (sub 2) ] (super 4-) that alternates with intersheets, randomly occurring in a ratio ideally 1:1, of type 1 [(Ca, Mn (super 2+) ) (sub 2) SiO (sub 2) ] (super 4+) and of type 2 (Ca,Mn (super 2+) ) (sub 2) M2 (sub 2) (OH) (sub 2) O (sub 2) ] (super 4+) , where Fe (super 3+) and Mn (super 3+) populate 3/4 of the M1 site and Al the remaining 1/4, while V (super 3+) , Mg and Al occupy in nearly equal proportions the M2 site. The simplified formula, inferred from chemical analyses, structure refinement and crystal-chemical considerations, may be written as (Ca, Mn (super 2+) ) (sub 4) (Fe (super 3+) , Mn (super 3+) , Al) (sub 4) (OH) (sub 4) (V (super 3+) , Mg, Al) (sub 2) (O, OH) (sub 4) (SiO (sub 4) ) (sub 2) (Si (sub 3) O (sub 10) ). From the composition of the "dominant" end-member of the complex solid-solution the end-member formula Ca (sub 4) Fe (sub 4) (super 3+) (OH) (sub 4) V (sub 2) (super 3+) O (sub 2) (OH) (sub 2) (SiO (sub 4) ) (sub 2) (Si (sub 3) O (sub 10) ) may be proposed for cassagnaite. So, cassagnaite may be classified as sorosilicate with insular and triple tetrahedral groups and belongs to the ardennite group in Dana's classification.

ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 20
Serial Issue: 1
Title: Cassagnaite, a new, V-bearing silicate mineral from the Cassagna Mine, Northern Apennines, Italy
Affiliation: Universita di Genova, Dipartimento per lo Studio del Territorio e delle sue Risorse, Genoa, Italy
Pages: 95-100
Published: 200802
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Federal Republic of Germany
References: 14
Accession Number: 2008-072091
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 6 tables, geol. sketch map
N43°45'00" - N44°40'00", E07°45'00" - E10°04'60"
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 200819
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