tinguaite Petrogr.
(ˈtɪŋgwəaɪt)
[ad. G. tinguait (H. Rosenbusch Mikrosk. Physiogr. der massigen Gesteine (ed. 2, 1887) II. 628), f. Serra de Tinguá, name of a spur of the Serra do Mar, W. of Rio de Janeiro: see -ite1.]
A hypabyssal rock similar to phonolite and nepheline-syenite, composed essentially of alkali feldspar, nepheline, and ægirine (acmite), the last occurring usu. as acicular crystals and conferring a greenish colour.
| 1893 Mineral. Mag. X. 173 More markedly porphyritic types are a rock with porphyritic elæolite, an ‘elæolite tinguaite’ with porphyritic orthoclase. 1965 G. J. Williams Econ. Geol. N.Z. xi. 167/2 Among these rocks is a tinguaite consisting of a network of aegirine crystals with phenocrysts of anorthoclase in a groundmass of anorthoclase, cancrinite and nepheline. 1978 S. R. Nockolds in S. R. Nockolds et al. Petrol. for Students xv. 173 Some tinguaites have small amounts of a sodalite mineral, of analcite.., or of cancrinite. More rarely, one or other of these becomes an important constituent. |