Ijolite

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Ijolite (derived from the first syllable of the Finnish words Ji-waru, Jijoki, &c., common as geographical names in the Kola peninsula, and the Gr. Xiflos, a stone), is an igneous rock consisting essentially of nepheline and augite. Ijolite is a rare rock type of considerable importance from a mineralogical and petrological standpoint. It occurs in various parts of the Kola peninsula in north Finland on the shores of the White Sea.

The pyroxene is morphic, yellow or green, and is surrounded by formless areas of nepheline. The accessory minerals are apatite, cancrinite, calcite, titanite and jiwaarite, a dark-brown titaniferous variety of melanite-garnet. This rock is the plutonic and holo-crystalline analogue of the nephelinites and nepheline-dolerites; it bears the same relation to them as the nepheline syenites have to the phonolites. It is worth mentioning that a leucite-augite rock, resembling ijolite except in containing leucite in place of nepheline, is known to occur at Shonkin Creek, near Fort Benton, Montana, and has been called missourite.

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