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shonkinite A dark coloured, coarsegrained, igneous rock consisting of essential diopside (making up about 50% of the rock), alkali feldspar, and biotite, with or without olivine and/or nepheline. Where olivine or nepheline is abundant the rock name is prefixed with these mineral names (e.g. olivine-shonkinite). Shonkinites are essentially a type of alkali syenite.