Winchite and the actinolite–glaucophane miscibility gap
Leake et al.1 have recently emphasized the apparent scarcity of winchite s.l., NaCa(Mg, Fe2+)4(Al, Fe3+) [Si8O22/(OH)2] (ref. 2), an amphibole intermediate in composition between the glaucophane–riebeckite series of high-pressure blueschists and the tremolite–actinolite series of lower-pressure greenschists. The rarity of winchite is considered consistent with the existence of a miscibility gap3,4 between these two amphibole series at the metamorphic P–T conditions normally attained in nature. Here we present optical and X-ray properties of Mg- and Al-rich winchite from Venezuela and draw attention to several other recent winchite analyses. In fact, as Schliestedt's5 new data on co-existing sodic and calcic amphiboles in blueschists show, only the present Mg–Al-rich winchite definitely lies within the above miscibility gap.
Winchite from Mt. Hiei contact aureole, Kyoto, Japan
Sodic-calcic amphibole closely associated with aegirine-augite was newly found from a sandy hornfels at Mt. Hiei contact aureole, Kyoto, Japan. The amphibole shows a pleochroism of X=colorless, Y=blue and Z=light blue and is winchite with significant amounts of TiO2 (1.5-2.5 wt.%) and of Mg-Fe-Mn-Li amphibole component at B site (ca. 0.1-0.4 cations for O=23 basis). The chemical composition and the coexisting phases of the winchite in this study are similar to those in the alkaline igneous complex.
The Younger Intrusive Rocks of the Kudaru Hills, Nigeria
I. Introduction A Preliminary account of the geology of the Kudaru Hills was published in 1927 (Bain), but a more detailed study of the group has since been completed and is now presented. The discovery of fayalite in certain rocks has necessitated a modification in the terminology and order of intrusion given in the first account. The hills are in the Zaria Province of Nigeria, lying midway between the towns of Zaria and Jos on the railway (Fig. 1). The area is about 65 square miles and has an oval outline with the longer axis running north-east and south-west. The axes measure 11 miles and 7½ miles respectively. To the south, near Munchira, joined to the main mass of the hills by a low neck, is a prolongation of the main intrusion which rises to a considerable height in D. Nasalwa and which measures 2½ miles by 1 mile. Bordering the group on the north and east sides is a curved ridge containing some high peaks (Pl. VIII). Separating this ridge from the main part of the group is a crescent-shaped plain divided into two by a number of low hills west of Babinda village. This plain is underlain by various gneisses, while the rest of the district consists of later members of the Younger Intrusive series of the Northern Provinces of Nigeria (Falconer, 1923). The highest peaks are in the interior but not in the centre of the group, and bare massive ridges of solid granite are there developed,