Thortveitite

minerals

bastnasite

euxenite

monazite

Formula: Sc2Si2O7
Sorosilicate (Si2O7 groups), thortveitite group, scandium-bearing mineral
Specific gravity: 3.5
Hardness: 6 to 7
Streak: White
Colour: Greyish-green, black, grey, blue, yellow, brown
Solubility: Slightly soluble in boiling hydrochloric acid and also HF (Dana)
Common impurities: Zr,Hf,Al,Fe,Mn,Mg,Ca,Ce,TR
Environments

Pegmatites most often
Metamorphic environments sometimes
Hydrothermal environments

Thortveitite most often occurs in granite pegmatites, but also occurs in hydrothermal veins and sometimes in greisen (Dana).

Localities

At the Trimouns quarry, Luzenac, Ariege, France, thortveitite has been found associated with banded dolomite, also perched on crystals of bastnäsite with calcite and clinochlore (Minrec 35.3.243).

At Isanagomine, Japan, thortveitite has been found associated with kobeite, perrierite, tourmaline, euxenite, monazite, zircon, allanite, magnetite and ilmenite (HOM).

At Befanamo,Madagascar, thortveitite has been found associated with monazite, fergusonite, rutile variety ilmenorutile, beryl, muscovite and magnetite (HOM).

In north-eastern New Caledonia, in the south-west Pacific ocean, recrystallized zircon grains in a muscovite variety phengite - epidote - chlorite schist contain as inclusions a mineral assemblage of celadonite, kaolinite, quartz, smectite group minerals (which includes montmorillonite, saponite and nontronite), chlorite, xenotime-(Y), thortveitite, yttrialite-(Y) and allanite-(Ce). This assemblage formed during seafloor alteration of a plagioclase-rich mafic rock at a temperature below 100oC. It is suggested that thortveitite, yttrialite-(Y), and xenotime-(Y) formed as a result of trace-element expulsion from zircon during low-temperature recrystallisation (AM 89.1795-1806).

At the type locality, Ljosland 04, Knipan, Iveland, Aust-Agder, Norway, thortveitite has been found in small granite pegmatite dikes. The paragenetic succession is euxenite, monazite, zircon variety alvite, rutile variety ilmenorutile, thortveitite, beryl, magnetite, biotite, muscovite, albite variety oligoclase, microcline and quartz (AM 7.195-196, HOM).

At Crystal mountain, Darby, Ravalli county, Montana, USA, thortveitite has been found as grains included in fluorite (Dana).

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