Oberti, R; Boiocchi, M; Hawthorne, FC; Ball, NA; Camara, F; Pagano, R; Pagano, A; ,
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)square Ca-B(2)C(Fe42+Fe3+)T(Si7Al) O-22 W(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)(Sigma=0.23) (B)(Ca1.93Na0.07)(Sigma=2.00) (C)(Mg1.16Fe3.212+Mn0.06Fe0.453+Al0.12Ti0.01)(Sigma=5.01) (T)(Si7.26Al0.74)(Sigma=8.00) O-22 (W)(OH1.89F0.01Cl0.10)(Sigma=2.00). Ferro-ferri-hornblende is biaxial (-), with alpha = 1.697(2), beta = 1.722(5), gamma = 1.726(5) and 2V (meas.) = 35.7(1.4)degrees, 2V (calc.) = 43.1 degrees. The unit-cell parameters are a = 9.9307(5), b = 18.2232(10), c = 5.3190(3) angstrom, beta = 104.857(1)degrees, V = 930.40 (9) angstrom(3), 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 angstrom), I, (hkl)] are: 8.493, 100, (110); 2.728, 69, (151); 3.151, 47, (310); 2.555, 37, ((2) over bar 02); 2.615, 32, (061); 2.359, 28, ((3) over bar 51); 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, Universita 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.
Physical Sciences - Other Topics; ferro-ferri-hornblende, electron-microprobe analysis, crystal-structure; refinement, Traversella mine, Italy; nomenclature