Outstanding grey crystals of the rare mineral delhayelite from a Russian locality (Rasvumtchorr, Khibiny, Kola, Russian Federation). — Photo: David Hospital · CC BY-SA 4.0
Delhayelite
Delhayelite is an IMA-recognized mineral species in the silicate class, with the chemical formula K₇Na₃Ca₅Al₂Si₁₄O₃₈F₄Cl₂.
It crystallizes in the orthorhombic crystal system (space group Pmmn). It is a member of the Rhodesite structural group.
Key properties: specific gravity 2.6; optically biaxial.
IMA symbol Dhy, IMA status: approved, named in 1959.
Found in a kalsilite-bearing melilite-nepheline lava (Mt. Shaheru, Congo).
It is found associated with Kalsilite, nepheline, gÄotzenite, combeite, kirschsteinite (Mt. Shaheru, Congo); fenaksite, eudialyte, lomonosovite (Khibiny massif, Russia).
The mineral was named to honor Fernard Delhaye (1880–1946), Belgian geologist, a pioneer in the geological exploration of the northern Kivu region of Congo (Zaire).