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GEOREF RECORD

Capranicaite, (K,[])(CaNa)Al (sub 4) B (sub 4) Si (sub 2) O (sub 18) ; a new inosilicate from Capranica, Italy, with a peculiar topology of the periodic single chain [Si (sub 2) O (sub 6) ]

Athos Maria Callegari, M. Boiocchi, F. Bellatreccia, E. Caprilli, O. Medenbach and A. Cavallo
Capranicaite, (K,[])(CaNa)Al (sub 4) B (sub 4) Si (sub 2) O (sub 18) ; a new inosilicate from Capranica, Italy, with a peculiar topology of the periodic single chain [Si (sub 2) O (sub 6) ]
Mineralogical Magazine (February 2011) 75 (1): 33-43

Abstract

Capranicaite, ideally (K,[])(Ca,Na)Al (sub 4) B (sub 4) Si (sub 2) O (sub 18) , is a new inosilicate mineral from the Vico volcanic complex collected at Capranica, Viterbo Province, Latium, Italy. It occurs in miarolitic cavities of a feldspathoid-bearing syenite ejectum and formed by late-stage metasomatic processes related to the activity of the Vico volcano. Capranicaite occurs as thin, tabular crystals no larger than 0.1 mm. Crystals are colourless, with a white streak and a vitreous lustre; they are brittle and their Mohs hardness is certainly <6. Capranicaite is non-fluorescent with good {001} cleavage and no observable parting. The calculated density is 2.41 g/cm (super 3) . Crystals are biaxial negative, non pleochroic, with alpha =1.495(1), beta =1.543(1), gamma =1.544(1), 2V (sub obs) =7.3(2) degrees , 2V (sub calc) =16.0 degrees . Capranicaite is monoclinic P2 (sub 1) /n, with a=4.8507(2), b=16.6156(6), c=20.5445(7) Aa, beta =90.245(1) degrees , V=1655.82(17) Aa (super 3) , Z=4. The strongest six X-ray diffraction lines in the simulated powder pattern are [d in Aa (I) (hkl)]: 3.234 (10) (124; 044), 4.104 (9) (121; 121), 3.424 (8) (006), 2.184 (4) (048; 164), 2.405 (4) (160), 2.425 (3) (200). EMP-WDS analysis gives: SiO (sub 2) 20.70, Al (sub 2) O (sub 3) 32.91, B (sub 2) O (sub 3) 22.90, K (sub 2) O 5.36, CaO 11.04, Na (sub 2) O 4.08, Cs (sub 2) O 2.20, sum 99.19%; the formula, based on 18 oxygens, is: (K (sub 0.69) Cs (sub 0.10) ) (sub Sigma 0.79) (Ca (sub 1.19) Na (sub 0.80) ) (sub Sigma 1.99) Al (sub 3.91) B (sub 3.99) Si (sub 2.09) O (sub 18) , corresponding to the ideal formula: (K,[])(Ca,Na)Al (sub 4) B (sub 4) Si (sub 2) O (sub 18) . The crystal structure shows three overlapping layers of polyhedra parallel to (001): (1) the A layer contains periodic single chains formed by Si (sub 2) O (sub 6) units with a topology not previously observed; (2) the B layer contains isolated AlO (sub 4) tetrahedra and BO (sub 3) triangles forming a sheet of six-fold rings (3Al+3B); (3) the C layer contains two octahedral sites: M(1) and M(2), with a mixed (Ca, Na) population. Two B layers and an intermediate A layer are vertex-connected to form a bi-dimensional B-A-B network characterized by large channels not completely populated and accommodating K and minor Cs. Along c from the origin the following layer sequence results: C-[B-A-B]-C-[B-A-B]-C.


ISSN: 0026-461X
EISSN: 1471-8022
Coden: MNLMBB
Serial Title: Mineralogical Magazine
Serial Volume: 75
Serial Issue: 1
Title: Capranicaite, (K,[])(CaNa)Al (sub 4) B (sub 4) Si (sub 2) O (sub 18) ; a new inosilicate from Capranica, Italy, with a peculiar topology of the periodic single chain [Si (sub 2) O (sub 6) ]
Affiliation: Universita di Pavia, Dipartimento di Scienze della Terra, Pavia, Italy
Pages: 33-43
Published: 201102
Text Language: English
Publisher: Mineralogical Society, London, United Kingdom
References: 36
Accession Number: 2011-046165
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 7 tables
N41°13'60" - N42°49'60", E11°30'00" - E14°00'00"
Secondary Affiliation: Universita di Roma Tre, ITA, ItalyRuhr-Universitaet Bochum, DEU, GermanyIstituto Nazionale di Geofisica e Vulcanologia, ITA, Italy
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201126
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