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Formula: Y2Fe2+Be2O2(SiO4)2
Nesosilicate (insular SiO4 groups),
gadolinite subgroup,
gadolinite group,
gadolinite supergroup,
yttrium-bearing mineral
Crystal System: Monoclinic
Specific gravity: 4.36 to 4.77 measured, 4.41 calculated
Hardness: 6½ to 7
Streak: Greenish grey
Colour: Black, greenish black, brown
Solubility: Gelatinises in acids, especially if metamict, dissolves with difficulty on heating in hydrochloric acid
(Dana)
Slightly RADIOACTIVE
Environments
Plutonic igneous environments
Pegmatites
Hydrothermal environments
Gadolinite-(Y) is often slightly radioactive due to minor uranium and/or thorium content, and therefore it is
often metamict. It occurs most often in alkaline granitic
pegmatites or
granite, rich in alkaline earth elements, and also in alpine-type
veins
(Dana, Webmin),
associated with allanite,
fluorite,
fergusonite,
yttrialite-(Y),
chevkinite and zircon
(HOM, Mindat).
Localities
At Mount Tanakami, just east of Kyoto, Shiga Prefecture, Japan, gadolinite-(Y) has been reported from
pegmatites
(R&M 84.6.523).
The type locality is Ytterby, Resarö, Vaxholm, Stockholm, Sweden.
In the UK gadolinite-(Y) and fergusonite-(Y) have been reported from the
granitic Mourne mountains in north east Ireland, and in
granite in Arran, Strathclyde, Scotland (JRS 14.23-25).
At Mount Rosa, El Paso county, Colorado, USA, beryl is absent, but late-stage
to secondary beryllium-bearing minerals
are present. Crystals of gadolinite to 1 mm have been collected from a miarolitic cavity associated
with smoky quartz, microcline,
zircon and kainosite-(Y)
(R&M 95.3.271-272).
At Fairview, Stove Mountain, El Paso County, Colorado, USA, miarolitic cavities host gadolinite-(Y) crystals
that are dark green and associated with crystals of smoky quartz,
microcline, zircon and
kainosite
(R&M 97.5.418).
At the North Sugarloaf Mountain locality, Bethlehem, Grafton County, New Hampshire, USA, gadolinite-(Y) was
found with fluorite and
bastnäsite-(Ce). The brown crystals are only a few mm in length, and form
radiating groups up to 3 cm across
(R&M 97.3.220-221).
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