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V.—The Crawfordjohn Essexite and Associated Rocks

Published online by Cambridge University Press:  01 May 2009

Extract

Another type, which is found in both quarries and which under the microscope has the aspect of a monchiquite or limburgite,. probably represents the actual marginal rock of the intrusion. It consists of small microphenocrysts of augite and olivine in a dark matrix, which can be resolved into granular augite and magnetite in a nearly isotropic base. The latter, which sometimes contains felspar microlites, seems to be mainly analcite with some nephelite, as it can be readily gelatinized and stained, while the refractive index is very low. The felspar microlites are small and sometimes have a rough trachytic structure resembling that of the mugearites. Following Harker's suggestion that augite-olivine rocks with an isotropic base should be classed as limburgites when the base is glass and as monchiquites when it is analcite, this rock can be included in the latter, group. The parts which are richer in felspar may be termed analcite-basalts.

Type
Original Articles
Copyright
Copyright © Cambridge University Press 1915

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References

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