Bostonite, associated with, but earlier than, the composite sill at Rudh'a' Chromain, on Mull, off the west coast of Scotland, shows alkali feldspar, iron ore, calcite, clinopyroxene, chlorite, and quartz. It contains a black limestone xenolith thought to be of lower Liassic (lower Jurassic) age. The results of chemical and spectrographic analyses and normative data are tabulated.

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