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teschenite An undersaturated, medium-to coarse-grained, igneous rock consisting of essential calcium-plagioclase, analcime, titanaugite, and barkevikite, with accessory iron oxide. The rock is similar to essexite but with analcime taking the place of nepheline. The teschenite of the Lugar sill, in Ayrshire, Scotland, is a well-known British example.