Vlasovite

vlasovite

arfvedsonite

gittinsite

eudialyte

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Formula: Na₂ZrSi₄O₁₁
Inosilicate (chain silicate), zirconium-bearing mineral
Crystal System: Monoclinic
Specific gravity: 2.92 to 2.97 measured, 3.07 calculated
Hardness: 6
Streak: White
Colour: Colourless, honey-brown
Environments

Pegmatites
Metamorphic environments

Vlasovite occurs as a late phase in nepheline syenite, syenitic pegmatites, and along the contact zone of a differentiated alkalic massif (Webmin). Vlasovite forms as a magmatic accessory or by metamorphism of elpidite (CM 23.577-582). Associated minerals include eudialyte, microcline, albite, lorenzenite, arfvedsonite, magnesium-rich katophorite, aegirine, aenigmatite, fayalite, pyrochlore, apatite and fluorite (HOM).

Localities

At the Villedieu Township, Les Lacs-du-Témiscamingue, Témiscamingue RCM, Abitibi-Témiscamingue, Quebec, Canada, the commonest occurrence of vlasovite is as sub-rounded grains from 1-2 cm across surrounded by red eudialyte in a rock composed of K-feldspar, vlasovite, eudialyte, mosandrite and alkali-rich amphibole. The vlasovite is separated from the eudialyte by a thin rind of gittinsite. Less common are crystals of vlasovite up to 15 cm in length set in a matrix of K-feldspar and eudialyte (CM 12.211-214, CM 44.1349-1356).

At the type locality, Vavnbed Mountain, Lovozersky District, Murmansk Oblast, Russia, vlasovite occurs in the contact zone between pegmatites and fenites. It was formed in areas of strongly microclinised and albitised rock by replacement of eudialyte. Associated minerals include microcline, albite, arfvedsonite, aegirine, eudialyte, apatite and fluorite (AM 46.1202-1203).

At Ascension Island, Saint Helena, Ascension and Tristan da Cunha, vlasovite occurs in miarolitic cavities in ejected blocks of peralkaline granite (HOM).

Alteration

elpidite to vlasovite, SiO₂ and H₂O
Na₂ZrSi₆O₁₅.3H₂O ⇌ Na₂ZrSi₄O₁₁ + 2SiO₂ + 3H₂O
(CA 23.577-582).

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