Images
Formula: (Y,REE,Ca,Na)15(Al,Fe3+)CaxAs3+1-x(Si,As5+)Si6B3(O,F)48
Nesosilicate (insular SiO4 groups), vicanite group
Crystal System: Trigonal
Specific gravity: 5.206 calculated
Hardness: 5 to 6
Colour: Pale brown
Weakly RADIOACTIVE
Environments
Localities
The type locality is Hundholmen, Narvik, Nordland, Norway.
Hundholmenite-(Y) has been found in granitic pegmatites at Stetind, Tysfjord, Nordland County, north
Norway, Lagmannsvik, Hamarøy, Nordland, and Hundholmen, Tysfjord, Nordland.
The description of the new mineral was based on material from Hundholmen, which consequently became
the type locality.
The Hundholmen granitic
pegmatite is a very large
pegmatite that has been mined extensively for
K-feldspar, quartz and
fluorite. It is known for cm-sized crystals of
thalénite-(Y) and non-metamict
gadolinite. Hundholmenite-(Y) from Hundholmen occurs as grains or
crystals up to 1 mm in size, forming aggregates up to 3 mm across. It is embedded in massive REE-bearing
fluorite. The only closely associated mineral is
allanite-(Ce). In the Stetind occurrence, hundholmenite-(Y) forms
mm-sized crystals, embedded in REE-bearing fluorite. Other accessory minerals
in the massive fluorite include
bastnäsite-(Ce),
britholite-(Y),
törnebohmite-(Ce),
rowlandite-(Y),
allanite-(Ce),
yttrialite-(Y) and
thalénite-(Y). At the Lagmannsvik occurrence, hundholmenite-(Y)
occurs as tiny crystals in a REE-bearing fluorite matrix or as small
aggregates along joints. The crystallisation of the fluorite and associated
minerals took place at a late stage of the pegmatite formation,
so hundholmenite-(Y) is a late-stage, primary
pegmatite mineral. Other REE minerals formed by
secondary alteration of minerals such as
gadolinite-(Y) and REE-bearing
fluorite include tengerite-(Y),
kainosite-(Y), adamsite-(Y),
kamphaugite-(Y) and
calcioancylite-(Ce)
(MM 71(2).179–192).
Back to Minerals