White glassy granular crystals of the extremely rare mineral arctite from the type locality and only know locality worldwide (Vuonnemiok River Valley, Kola, Russian Federation), and associated to pink villiaumite. Ex-Excalibur-Cureton Company specimen. — Photo: David Hospital · CC BY-SA 4.0
Arctite
Arctite (Na2Ca4(PO4)3F) is a colourless mineral found in the Kola Peninsula northern Russia. Its IMA symbol is Arc. It has a Mohs hardness of 5 and has a specific gravity of 3.13. Arctite is transparent with a vitreous lustre. Arctite has a perfect cleavage and a trigonal crystal system. It is also a naturally occurring antiperovskite. Common associates of arctite include aegirine, natisite, lomonosovite, umbite and thenardite.
Intro adapted from Wikipedia (CC BY-SA).
Arctite is an IMA-recognized mineral species in the phosphate class, with the chemical formula (Na₅Ca)Ca₆Ba(PO₄)₆F₃.
It crystallizes in the hexagonal crystal system (space group R-3m).
Key properties: Mohs hardness 5; specific gravity 3.13; Vitreous, pearly on the perfect cleavage luster; optically uniaxial.
IMA symbol Arc, IMA status: approved, named in 1980.
A late-stage pneumatolytic mineral in pegmatitic veinlets in a differentiated alkalic massif.
It is found associated with Natrosilite, vuonnemite, lomonosovite, zirsinalite, natisite, rasvumite, villiaumite, aegirine, thenardite, umbite, paraumbite, kostylevite, wadeite.
The name is derived from the locality in the Arctic region.