Pinkish white crystal group of the rare titanium mineral penkvilksite from the type locality: Yubileinaya Pegmatite, Lovozero Massif, Kola, Russian Federation. — Photo: David Hospital · CC BY-SA 4.0
Penkvilksite
Penkvilksite is an IMA-recognized mineral species in the silicate class, with the chemical formula Na₂TiSi₄O₁₁·2H₂O.
It crystallizes in the orthorhombic crystal system (space group Pnca).
Key properties: Mohs hardness 5; specific gravity 2.58; Pearly or silky on fresh fracture; dull on the surface luster; optically biaxial.
IMA symbol Pvl, IMA status: approved, named in 1973.
Found in the central natrolite zone of a pegmatite in a differentiated alkalic massif (Lovozero massif, Russia); in a pegmatite vein and in a marble xenolith in an intrusive alkalic gabbro-syenite complex (Mont Saint-Hilaire, Canada).
It is found associated with Aegirine, natrolite, mountainite, raite (Lovozero massif, Russia); microcline, aegirine, catapleiite, ancylite, nenadkevichite, pectolite, apophyllite.
The name comes from the Lapp penk, for curly, and vilkis, for white, for its typical appearance.