Formula: Sc2Si2O7
Sorosilicate (Si2O7 groups), thortveitite group,
scandium-bearing mineral
Crystal System: Monoclinic
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-(Y),
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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