Formula: Y2SiO4)(CO3)
Yttrium-bearing nesosilicate (insular SiO4 groups)
Specific gravity: 4.47
Hardness: 5½ to 6
Streak: White
Colour: Buff to tan, white to pale cream, yellow
Solubility: Slightly soluble in cold hydrochloric acid



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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