Formula: Y2SiO4)(CO3)
Nesosilicate (insular SiO4 groups), yttrium-bearing mineral
Crystal System: Triclinic
Specific gravity: 4.47 measured, 4.91 calculated
Hardness: 5½ to 6
Streak: White
Colour: Buff to tan, white to pale cream, yellow
Solubility: Slightly soluble in cold hydrochloric acid
Environments
Localities
At the Tremouns quarry, France, iimoriite-(Y) occurs in dolomite, and sometimes in vugs
in talc. It is commonly associated with thortveitite
and is found in the same environment as hingganite
(MinRec 35.3.238-239).
At the type locality, Fusamata, Kawamata, Fukushima, Japan, iimoriite-(Y) occurs as an alteration product of
thalénite-(Y) in a quartz -
microcline pegmatite. Associated minerals include
biotite, monazite,
fergusonite and torbernite. Iimoriite is
also known from the nearby Suishoyama (formerly Iisaka) pegmatite as an alteration product of
thalénite-(Y).
(AM 58.140, Dana).
On the Kola Peninsula, Murmansk Oblast, Russia, iimoriite-(Y) occurs in amazonite
- zinnwaldite pegmatite with fluorite,
thalénite-(Y),
keiviite-(Y) and
vyuntspakhkite-(Y)
(Dana).
At Bokan mountain, Prince of Wales Island, Alaska, USA, iimoriite-(Y) occurs in a thorite
and uraninite bearing quartz and
albite vein emplaced into peralkaline riebeckite
and aegirine bearing granite.
Quartz and albite are the principal
gangue minerals.
Iimoriite has been found in only two places in the vein, associated with siderite.
Yttrium-group rare earths predominate in the samples where iimoriite was recovered, and yttrium makes up at least 2% of each
bulk sample
(AM 69.196, Dana).
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