IJOLITE (derived from the first syllable of the Finnish words Jiivaru, Jijoki, etc., common as geographical names in the Kola peninsula, and the Gr. Xi0os, a stone), a rock consisting essentially of nepheline and augite, and of great rarity, but of considerable importance from a mineralogical and petrographical 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 nephelenites and nepheline-dolerites; it bears the same relation to them as the nepheline-syenites have to the phonolites. It is worth mentioning that a leuciteaugite 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.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)