This is the polished on the one side greenish-gray tinguaite specimen. Dimensions: 1.8 x 1.7 x 0.9″ (4.5 x 4.2 x 2.3cm). Weight — 2.5oz (70 grams). Origin: Russia, Kola Peninsula.
Some information about tinguaite:
Tinguaite is an undersaturated, medium-to coarse-grained, igneous rock consisting of essential alkali feldspar, nepheline, and aegirine (with or without sodic amphibole or biotite). Tinguaite is the hypabyssal equivalent of phonolite.