Hundholmenite-(Y)

hundholmenite-(Y)

allanite-(Ce)

bastnasite-(Ce)

britholite-(Y)

Images

Formula: (Y,REE,Ca,Na)15(Al,Fe3+)CaxAs3+1-x(Si,As5+) Si6B3(O,F)48
Nesosilicate (insular SiO4 groups), vicanite group
Specific gravity: 5.206
Hardness: 5 to 6
Colour: Pale brown
Weakly RADIOACTIVE
Environments

Pegmatites

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).

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