. Bulletin of the British Museum (Natural History), Mineralogy. VOLCANIC ROCKS FROM THE CAPE VERDE ISLANDS 43 size. Vesicles are of two kinds, one more or less circular and filled by calcite, the other ramifying irregularly through the groundmass into which they merge at their edges, and composed of zeolites and potash-soda feldspar (Fig. 6a). Bebiano (op. cit.: 205) records a phonolite containing biotite along with haiiyne and sphene at M. Vizia, 200 metres west of Furna, Brava, with large phenocrysts of. Fig. 6. (a) Biotite-rich haiiyne-phonolite. N. of Furna, Brava [8]. (b) Hornblende-trach
. Bulletin of the British Museum (Natural History), Mineralogy. VOLCANIC ROCKS FROM THE CAPE VERDE ISLANDS 43 size. Vesicles are of two kinds, one more or less circular and filled by calcite, the other ramifying irregularly through the groundmass into which they merge at their edges, and composed of zeolites and potash-soda feldspar (Fig. 6a). Bebiano (op. cit.: 205) records a phonolite containing biotite along with haiiyne and sphene at M. Vizia, 200 metres west of Furna, Brava, with large phenocrysts of. Fig. 6. (a) Biotite-rich haiiyne-phonolite. N. of Furna, Brava [8]. (b) Hornblende-trachyte. R. da Torre, S. Antao [520] feldspar in a groundmass of microlites of aegirine-augite, nepheline, and orthoclase, with biotite, haiiyne, and sphene. The feldspar is said to include oligoclase. Blocks in the phonolite agglomerate. The ' blocks' and ' clots' of rocks resembling the sanidinites of the Eifel district referred to above (p. 36) are from the phonolite agglomerates of Brava, Child's description of the locality being ' cliffs near cave at mouth of Rio Lacacan'. Several of the specimens are haiiyne-sanidinites, contain- ing ' clots' mainly of haiiyne with reticulated inclusions of iron ores usually in zones, and variable amounts of sanidine with or without a little albite-oligoclase. The inter- stices between these crystals are filled with phonolitic base or nests of aegirine needles, iron ore, and glass. [71, 72.] [67], from the same locality, is another coarse 'clot' composed of aegirine-augite, magnetite, haiiyne, biotite (in parts mainly replaced by magnetite), and apatite. The finer parts of the specimen are composed mainly of haiiyne with scattered ragged pyroxenes. These minerals enclose poecilitically a mesh of apatite prisms, which in the coarser portions occurs also in radiating tufts (Fig. ya). The pyroxene has a 1727, y 1745. [115] from the phonolite tuffs, i km. west of 'Povoagao', Brava, is a 'clot' of. Please note that these images are extracted
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