Fluorcalciomicrolite
Fluorcalciomicrolite is an IMA-recognized mineral species in the halide class, with the chemical formula (Ca,Na, )₂Ta₂O₆F.
It crystallizes in the cubic crystal system (space group Fd-3m). It is a member of the Pyrochlore-microlite structural group.
Key properties: Mohs hardness 4–5; specific gravity 6.16; White streak; Adamantine to resinous luster.
IMA symbol Fcmic, IMA status: approved, named in 2012.
Found in heavy mineral concentrates from a rare-element granitic pegmatite exceptionally enriched in lithium and rubidium.
It is found associated with Microcline, albite, quartz, muscovite, spodumene, “lepidolite, ” cassiterite, tantalite-(Mn), monazite-(Ce), fluorite, “apatite, ” beryl, “garnet, ” epidote.
The name refers to a member of the microlite group with dominant fluorine in the Y structural site and calcium in the A structural site.