Astrophyllite Locality: Khibiny Massif , Kola Peninsula , Murmanskaja Oblast', Northern Region , Russia ( Locality at mindat.org ) Size: 6.9 x 6.2 x 1.9 cm. A particularly fine specimen from this important locality with thick, metallic-foil-like, flat-laying crystals to 3 cm embedded in matrix. Ex. Martin Zinn Collection. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Astrophyllite
A rare bronze to golden titanium-bearing silicate that forms star-like bladed crystal sprays — its name means 'star leaf'.
Intro adapted from Wikipedia (CC BY-SA).
Astrophyllite is an IMA-recognized mineral species in the silicate class, with the chemical formula K₂NaFe²⁺₇Ti₂(Si₄O₁₂)₂O₂(OH)₄F.
It crystallizes in the triclinic crystal system (space group P-1). It is a member of the Astrophyllite-Astrophyllite structural group.
Key properties: Mohs hardness 3; specific gravity 3.2–3.4; Golden streak; Submetallic, pearly, greasy luster; refractive index 1.703; optically biaxial.
IMA symbol Ast, grandfathered status — known before the IMA’s founding, named in 1848.
Found in nepheline syenites, alkali granites, and their pegmatites; less commonly in fenites and other metasomatized rocks; in nepheline syenite gneisses and paragneisses.
It is found associated with Albite, aegirine, arfvedsonite, nepheline, natrolite, zircon, biotite, leucophanite, eudialyte, catapleiite, djerfisherite, rasvumite, delhayelite, kupletskite.
Its name comes from the Greek for star and leaf, for the stellate and foliated micaceous habit.