TINGUAITE

pale- to dark-green, very fine-grained igneous rock that may be considered the dike (tabular body injected in fissures) equivalent of phonolite. It contains alkali feldspar and nepheline, with aegirine or aegirinaugite. Tinguaite in which the amount of feldspathoid (nepheline) equals or is greater than that of feldspar has a characteristic texture: the light-coloured matrix (groundmass) is equigranular and sugary, with needles of aegirine between and randomly crossing the other constituents to give a feltlike appearance. Notable sites of occurrence for tinguaite include Rio de Janeiro, Braz.; Hedrum, Nor.; and the Bearpaw Mountains of Montana in the United States.