Crystal structure of mineral fibres. 3. Actinolite asbestos

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Marco E. Ciriotti
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Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy

Crystal structure of mineral fibres. 3. Actinolite asbestos

Messaggio da Marco E. Ciriotti » ven 01 set, 2017 11:08

▪ Pollastri, S., Gigli, L., Ferretti, P., Andreozzi, G.B., Bursi Gandolfi, N., Pollok, K., Gualtieri, A.F. (2017): The crystal structure of mineral fibres. 3. Actinolite asbestos. Periodico di Mineralogia, 86, 89-98.

The present work reports chemical and structural data of actinolite asbestos from Aurina Valley, Bolzano (Italy). The chemical composition was determined using EMPA and TG analysis, and the Fe3+/Fetot ratio was accurately evaluated with independent 57Fe Mössbauer spectroscopy. Morphology and crystallinity were also investigated through SEM and TEM investigations. Crystal structure was refined using high-resolution synchrotron XRPD data. The iron content of Aurina Valley sample is lower compared to two representative asbestiform actinolite samples (with structure refinement) taken from the literature (FeOtot 7.77 wt% against 12÷13 wt%, respectively), accounting for the reduced cell volume here measured (910.29 Å. against 912÷918 Å., respectively). Refined site scattering values of Aurina Valley sample are in agreement with those calculated from chemical compositions, and the optimized structural formula is:
K0.02Na0.05(Na0.08Ca1.92)Ʃ=2.00(Mg3.80Fe2+0.79Fe3+0.11Al0.20Mn0.05Ni0.02Cr0.01)Ʃ= 4.98(Si7.67Al0.25)Ʃ=7.92O21.69(OH)2.31.
The C sites M(1), M(2) and M(3) are occupied by Mg and Fe in a proportion of ~4:1, whereas the M(4) site contains mainly Ca and a very small amount of Na. Iron exclusively occupies the octahedral C sites, with Fe2+ ions occurring at the M(1,2,3) sites and the small amount of Fe3+ (13% of Fetot) ordered at the M(2) site. The refined crystal structure and cation distribution are fully consistent with results previously obtained on asbestiform and non-asbestiform samples belonging to the tremolite-actinolite-ferro– actinolite substitutional series.
Marco E. Ciriotti

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