Abstract

This paper presents electron microprobe analyses of the type specimen of “freyalite”, a REE-Th mineral found in a nepheline syenite pegmatite of the Langesundfjord district (S. E. Norway). Freyalite was previously assumed to be related to thorite, but these data indicate that it is more accurately described as a thorian melanocerite (caryocerite) which has been altered with subsequent leaching of Na, Ca and F. The composition of the material may be expressed by the formula (RE, Ca, etc.)x(B, Si, etc.)3(O, OH, F)13. In an analysis of the least altered part of the specimen x = 4.017: (RE1.870y0.167Th0.413Zr0.104Ca1.129Fe0.095Na0.239) (B1Si1.823P0.159S0.019) (O7.067OH3.176F2.757) (boron and hydroxyl contents estimates only). This evidence discredits the name “freyalite”. The crystalline precursor of the metamict melanocerite was probably a boron- and fluorine-rich member of the mosandrite–gotzenite or cerite groups.

The Subcommission on New Minerals and Mineral Names of the International Mineralogical Association has approved the discreditation of “freyalite”.

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