Formula: LaF3
Fluoride of lanthanum
Crystal System: Trigonal
Specific gravity: 5.93 measured, 5.94 calculated
Hardness: 4 to 5
Streak: White
Colour: Greenish yellow
Weakly RADIOACTIVE
Environments
Plutonic igneous environments
Hydrothermal environments
Fluocerite-(La) occurs in hydrothermal
quartz veins in granite
(Webmin, HOM).
Localities
At the type locality, Zhanuzak, Kent Massif, Karkaraly, Karaganda Region, Kazakhstan, Fluocerite-(La) occurs in
hydrothermal quartz veins in
granite
(HOM).
The Wellington Lake pegmatite, Park county, Colorado, USA, is a
niobium-yttrium-fluorine type
pegmatite, known for its unusual rare-earth-element
enrichment, and hosted in granite. Major constituents of the
pegmatite are
quartz, perthite,
cleavelandite, iron oxides and
biotite. Accessory minerals include fluocerite,
bastnäsite, columbite,
cyrtolite and minor uranium-thorium species. Well developed tabular crystals
of fluocerite are epitaxially overgrown by bastnäsite, and occur in a matrix of irone-oxide boxwork associated
with quartz crystals. The
bastnäsite overgrowth is
zoned with respect to rare-earth elements and exhibits linear bands of enrichment in
neodymium, samarium,
gadolinium and yttrium.
The fluocerite-bastnäsite crystals
appear to be late in the paragenesis
(R&M 91-4.371-373).
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