Borolanite is an historicalpetrological name for apyroxene-melanite bearingnepheline syenite variety which containsnepheline-alkali feldsparpseudomorphs interpreted to be afterleucite which occur as conspicuous white spots in the dark rock matrix.[1] The rock occurs in the Borralan Igneous Complex or Loch Borralan Complex which is an alkalic igneous complex nearLoch Borralan in northwestScotland.[2][3]
The1911 Britannica described borolanite as: one of the most remarkablerocks of theBritish Isles, found on the shores of Loch Borolan (Loch Borralan) inSutherland, after which it has been named. In this locality there is a considerable area ofgranite rich in redalkalifeldspar, and passing, by diminution in the amount of itsquartz, into quartz-syenites and syenites. At the margins of the outcrop patches of nepheline syenite occur; usually the nepheline is decomposed, but occasionally it is well-preserved; the other ingredients of the rock are browngarnet (melanite) andaegirine. The abundance of melanite is very unusual inigneous rocks, though some syenites, leucitophyres, and aegirine-felsites resemble borolanite in this respect. In places the nepheline syenite assumes the form of a dark rock with large rounded white spots. These last consist of an intermixture of nepheline orsodalite and alkali-feldspar. From the analogy of certain leucite syenites which are known inArkansas, it is very probable that these spots represent originalleucites which have been changed intoaggregates of the above-namedminerals. They resemble leucite in their shape, but have not yet been proved to have itscrystalline outlines. The pseudo-leucites, as they have been called, measure one-quarter to three-quarters of an inch across. The dark matrix consists ofbiotite, aegirine-augite and melanite. Connected with the borolanite there are other types of nepheline syenite andpegmatite. InFinland, melanite bearing nepheline rocks have been found and described asijolite, but the only other locality for melanite-leucite-syenite isMagnet Cove igneous complex in Arkansas.[4]
One or more of the preceding sentences incorporates text from a publication now in thepublic domain: Flett, John Smith (1911). "Borolanite". InChisholm, Hugh (ed.).Encyclopædia Britannica. Vol. 4 (11th ed.). Cambridge University Press. p. 267..jpg) | This article aboutigneous petrology is astub. You can help Wikipedia byexpanding it. |