Fluornatromicrolite Locality: Darra-i-Pech (Pech; Peech; Darra-e-Pech) Pegmatite Field, Nangarhar (Ningarhar) Province , Afghanistan ( Locality at mindat.org ) Size: 4.4 x 3.7 x 2.6 cm. An incredible, gemmy, sharp, glassy 8mm fluornatromicrolite. This is from a small find of 3 years ago (2005-2006), and they seem to occur buried in lepidolite which must be removed to expose these hidden treasures. Extremely rare, beautiful and mineralogically significant specimens from this productive region. Ex. Laura and Stevia Thompson Collection. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Fluornatromicrolite
Fluornatromicrolite is an IMA-recognized mineral species in the halide class, with the chemical formula (Na₁.₅Bi₀.₅)Ta₂O₆F.
It crystallizes in the cubic crystal system (space group Fd3m). It is a member of the Pyrochlore-microlite structural group.
Key properties: Mohs hardness 5; specific gravity 6.49; White streak; Adamantine luster.
IMA symbol Fnmic, IMA status: approved, named in 1998.
Found in a granitic pegmatite.
It is found associated with Perthitic microcline, albite, amblygonite, muscovite, quartz, elbaite, tantalite-(Fe), tantalite-(Mn), beryl.
As a member of the microlite group with dominant fluorine (fluor) at an anion site and sodium (natro) in the A structural site.