High-resolution electron microscopy and diffraction studies of fibrous amphiboles

Fibrous specimens of tremolite, amosite, crocidolite and anthophyllite have been studied by electron diffraction and high-resolution microscopy. Amosite (and to a lesser extent crocidolite) are shown to be subject to frequent twinning on (100) leading to stacking disorder, and an explanation is provided of previously supposed anomalies in their diffraction patterns [Chisholm (1973), J. Mater. Sci. 8, 475-483]. Tremolite is sensibly free from these defects and this is explained in terms of crystal chemistry. The presence of Wadsley defects of the type suggested by Chisholm has been confirmed in tremolite, amosite and anthophyllite, and these defects have been shown to correspond to intercalation of lamellae of triple-chain structure parallel to (010). In anthophyllite these lamellae are observed to segregate into domains.