Schäferite

Schäferite is a rare vanadate mineral with chemical formula Ca₂NaMg₂[VO₄]₃. Schäferite is isometric, which means that it has three axes of equal length and 90° angles between the axes.^[4] Schäferite is isotropic, meaning that the velocity of light is the same no matter which direction the light passes through.^[3]

Schäferite
General
Category	Phosphate mineral Berzeliite group Garnet structural group
Formula	Ca2NaMg2[VO4]3
IMA symbol	Sfr[1]
Strunz classification	8.AC.25
Crystal system	Cubic
Crystal class	Hexoctahedral (m3m) H-M symbol: (4/m 3 2/m)
Space group	Ia3d
Unit cell	a = 12.427 Å, Z = 8
Identification
Formula mass	496.57 g/mol
Color	Red, orange-red
Crystal habit	Octahedral crystals
Cleavage	None
Fracture	Conchoidal
Mohs scale hardness	5
Luster	Vitreous
Streak	Yellow
Diaphaneity	Transparent
Optical properties	Isotropic
Refractive index	n = 1.96
References	[2][3]

It was named after Helmut Schäfer (born 1931) who discovered it in a quarry on the Bellerberg Volcano in Germany.^[2] It is found only in the Eifel Mountains volcanic area near Mayen, Laacher See district of Germany.^[2] It occurs within a xenolith in a leucite tephrite. It is the magnesium analogue of palenzonaite and is a member of the garnet structural group.^[3]