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Ijolite is anigneous rock consisting essentially ofnepheline andaugite.[1] Ijolite is a rare rock type of considerable importance from amineralogical andpetrological standpoint. The word is derived from the first syllable of the Finnish words such asIivaara,Iijoki · andIi, all geographical names inFinland, and theAncient GreekXiflos, a stone. Ijolite occurs in various parts of theKainuu region of easternFinland and in theKola Peninsula of northwestRussia on the shores of theWhite Sea.[2] Ijolite was first defined and named by Finnish geologistWilhelm Ramsay.[3]
Thepyroxene ismorphic[clarify], yellow or green, and is surrounded by formless areas of nepheline. The accessory minerals areapatite,cancrinite,calcite,titanite andschorlomite, a dark-brown titaniferous variety ofmelanite-garnet. This rock is theplutonic and holo-crystalline analogue of thenephelinites -volcanic equivalent and nepheline-dolerites; it bears the same relation to them as thenepheline syenites have to thephonolites.[2]
Aleucite-augite rock, resembling ijolite except in containing leucite in place of nepheline, is known to occur atShonkin Creek, nearFort Benton, Montana, and was earlier calledmissourite,[2] but is now regarded as a variety ofleucitite.[4]
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This article incorporates text from a publication now in thepublic domain: Chisholm, Hugh, ed. (1911). "Ijolite".Encyclopædia Britannica. Vol. 14 (11th ed.). Cambridge University Press. p. 298.