Hundholmenite-(Y)
Hundholmenite-(Y) is an IMA-recognized mineral species in the silicate class, with the chemical formula (Y,REE,Ca,Na)₁₅(Al,Fe³⁺)CaₓAs³⁺₁₋ₓ(Si,As⁵⁺)Si₆B₃(O,F)₄₈.
It crystallizes in the hexagonal crystal system (space group R3m). It is a member of the Okanoganite structural group.
Key properties: Mohs hardness 5–6; specific gravity 4.2; White streak; Vitreous to adamantine luster; optically uniaxial.
IMA symbol Hhm-Y, IMA status: approved, named in 2006.
A late-stage, primary mineral in granite pegmatite.
It is found associated with REE-bearing fluorite, allanite-(Ce).
The name refers to Hundholmen, Norway, where the studied samples were collected and a suffix for the dominant rare earth element.
Index entry. This entry combines official IMA/RRUFF species data with published physical-property data — a full written entry hasn’t been published yet.
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