Online Encyclopedia

LIMBURGITE

Online Encyclopedia
Originally appearing in Volume V16, Page 692 of the 1911 Encyclopedia Britannica.
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LIMBURGITE  , in

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petrology, a dark-coloured volcanic rock resembling
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basalt in appearance, but containing normally no felspar . The name is taken from Limburg (Germany), where they occur in the well-known rock of the Kaiserstuhi . They consist essentially of
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olivine and
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augite with a brownish glassy ground mass . The augite may be green, but more commonly is brown or
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violet; the olivine is usually pale green or colourless, but is sometimes yellow (hyalosiderite) . In the ground mass a second generation of small eumorphic augites frequently occurs; more rarely olivine is
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present also as an ingredient of the
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matrix . The
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principal
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accessory minerals are titaniferous iron oxides and
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apatite . Felspar though sometimes present is never abundant, and
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nepheline also is unusual . In some limburgites large phenocysts of dark brown
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hornblende and
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biotite are found, mostly with irregular
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borders blackened by resorption; in others there are large crystals of soda
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orthoclase or anorthoclase . Hauyne is an ingredient of some of the limburgites of the Cape Verde Islands.• Rocks of this
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group occur in considerable numbers in Germany (Rhine
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district) and in Bohemia, also in Scotland,
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Auvergne, Spain, Africa (
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Kilimanjaro), Brazil, &c . They are associated principally with basalts, nepheline and
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leucite basalts and monchiquites . From the last-named rocks the limburgites are not easily separated as the two classes bear a very close resemblance in structure and in
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mineral composition, though many authorities believe that the ground mass of the monchiquites is not a glass but crystalline
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analcite . Limburgites may occur as flows, as sills or dykes, and are sometimes highly vesicular .

Closely allied to them are the augitites, which are distinguished only by the

absence of olivine; examples are known from Bohemia, Auvergne, the Canary Islands, Ireland, &c .

End of Article: LIMBURGITE
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