Kogarkoite

Kogarkoite is a sodium sulfate fluoride mineral with formula Na₃(SO₄)F. It has a pale blue color, a specific gravity of about 2.67 and a hardness of 3.5. The crystal is monoclinic and is a type of naturally occurring antiperovskite. Kogarkoite is named after the Russian petrologist Lia Nikolaevna Kogarko (born 1936) who discovered the mineral.

Kogarkoite
General
Category	Sulfate mineral
Formula	Na3(SO4)F
IMA symbol	Kog[1]
Strunz classification	7.BD.15
Crystal system	Monoclinic
Crystal class	Pyramidal (2/m) (same H-M symbol)
Space group	P21/m
Unit cell	a = 18.07, b = 6.94 c = 11.44 [Å]; β = 107.72°; Z = 12
Identification
Color	Colorless, pale sky-blue, pale pink, lilac
Crystal habit	Tabular crystals, granular, earthy aggregates, pseudorhombohedral
Twinning	Common
Mohs scale hardness	3.5
Luster	Vitreous to dull
Streak	White
Diaphaneity	Transparent to translucent
Specific gravity	2.66
Optical properties	Biaxial (+)
Refractive index	nα = 1.439 nβ = 1.439 nγ = 1.442
Birefringence	δ = 0.003
2V angle	Small, approaching zero
Ultraviolet fluorescence	Cream to pale blue under SW UV and green under LW UV
Solubility	Slowly soluble in water
References	[2][3][4]

Discovery and occurrence

Kogarkoite was first described in 1973 for an occurrence on Alluaiv Mountain, Lovozero Massif, Kola Peninsula, Russia.^[3] On Alluaiv it occurs in pegmatitic veins in nepheline syenite. It occurs with sodalite in syenite xenoliths in an alkali intrusive complex at Mont Saint-Hilaire, Canada. In Hortense Hot Spring, Chaffee County, Colorado, it occurs as a sublimate.^[2] It occurs at Lake Natron near Ol Doinyo Lengai, Tanzania and Suswa Volcano, Lake Magadi, Kenya.^[2][3]

See also

• List of minerals
• List of minerals named after people