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Ferro-ferri-hornblende from the Traversella mine (Ivrea, Italy): occurrence, mineral description and crystal-chemistry

Published online by Cambridge University Press:  02 January 2018

Roberta Oberti ,
Massimo Boiocchi ,
Frank C. Hawthorne ,
Neil A. Ball ,
Fernando Cámara ,
Renato Pagano  and
Adriana Pagano
Roberta Oberti*
Affiliation:
CNR-Istituto di Geoscienze e Georisorse, UOS Pavia, via Ferrata 1, I-27100 Pavia, Italy
Massimo Boiocchi
Affiliation:
Centro Grandi Strumenti, Università degli Studi di Pavia, via Bassi 21, I-27100 Pavia, Italy
Frank C. Hawthorne
Affiliation:
Department of Geological Sciences, University of Manitoba, Winnipeg, MB, R3T 2N2, Canada
Neil A. Ball
Affiliation:
Department of Geological Sciences, University of Manitoba, Winnipeg, MB, R3T 2N2, Canada
Fernando Cámara
Affiliation:
Dipartimento di Scienze della Terra, Università degli Studi di Torino, via Valperga Caluso 35, I-10125 Torino, Italy CrisDi, Interdepartmental Centre for the Research and Development of Crystallography, via Giuria 5, I-10125, Torino, Italy
Renato Pagano
Affiliation:
Casella Postale 37, Cinisello (Mi), Italy
Adriana Pagano
Affiliation:
Casella Postale 37, Cinisello (Mi), Italy
*
*E-mail: [email protected]
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Abstract

Ferro-ferri-hornblende is a new member of the amphibole supergroup (IMA-CNMNC 2015-054). It has been found in a rock specimen from the historical collection of Leandro De Magistris, which was collected at the Traversella mine (Val Chiusella, Ivrea, Piemonte, Italy). The specimen was catalogued as ‘speziaite', and contains a wide range of amphibole compositions from tremolite/actinolite to magnesio-hastingsite. The end-member formula of ferro-ferri-hornblende is A□BCa2c(Fe+Fe3+)T(Si7Al) O22W(OH)2 , which requires SiO2 43.41, Al2O3 5.26, FeO 29.66, Fe2O3 8.24 CaO 11.57, H2O 1.86, total 100.00 wt.%. The empirical formula derived from electron microprobe analysis and single-crystal structure refinement for the holotype crystal is A(Na0.10K0.13) Σ=0.23B(Ca 1.93Na0.07)Σ=2.00C(Mg1.16Fe2+3.21Mn0.O6Fe3+0.45 Al0.12Ti 0.01)Σ=5.01T(Si7.26Al0. 74)Σ=8.00 O22W(OH1.89F0.01C10.10)Σ=2.00- Ferro-ferri-hornblende is biaxial (-), with α = 1.697(2), P = 1 .722(5), γ = 1.726(5) and 2V (meas.) = 35.7(1.4)°, 2V (calc.) = 43.1°. The unit-cell parameters are a = 9.9307(5), b = 18.2232(10), c = 5.3190(3) Å, β = 104.857(1)°, V= 930.40 (9) Å3, Z= 2, space group C2/m. The a:b:c ratio is 0.545:1:0.292. The strongest eight reflections in the powder X-ray pattern [d values (in Å), I, (hkl)] are: 8.493, 100, (110); 2.728, 69, (151); 3.151, 47, (310); 2.555, 37, (); 2.615, 32, (061); 2.359, 28, (); 3.406, 26, (131); 2.180, 25, (261). Type material is deposited in the collections of the Museo di Mineralogia, Dipartimento di Scienze della Terra e dell'Ambiente, Università di Pavia, under the catalogue number 2015-01. Sample M/U15285 from the historical collection of Luigi Colomba, presently at the Museo Regionale di Scienze Naturali di Torino, was also checked, and the presence of ferro-ferri-hornblende was confirmed.

Keywords

ferro-ferri-hornblendeelectron-microprobe analysiscrystal-structure refinementTraversella mineItaly
Type
Research Article
Information
Mineralogical Magazine , Volume 80 , Issue 7 , December 2016 , pp. 1233 - 1242
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2016

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