Fluoborite
Fluoborite found in Italy
General
Category	Borate mineral
Formula (repeating unit)	Mg3(BO3)(F,OH)3
IMA symbol	Fbo[1]
Strunz classification	6.AB.50
Crystal system	Hexagonal
Crystal class	Dipyramidal (6/m) H-M symbol: (6/m)
Space group	P63/m
Unit cell	a = 8.8612, c = 3.1021 [Å]; Z = 3
Identification
Formula mass	186.61 g/mol
Color	Colorless to violet or white
Crystal habit	Acicular, prismatic, stellate
Cleavage	Good on {0001}
Mohs scale hardness	3.5
Luster	Vitreous to silky
Streak	white
Diaphaneity	Translucent to transparent
Specific gravity	2.98
Optical properties	Uniaxial (−)
Refractive index	nω = 1.570 nε = 1.534
Birefringence	0.036
Ultraviolet fluorescence	Intense cream-white under SW UV
References	[2][3][4]

Fluoborite has a chemical formula of Mg₃(BO₃)(F,OH)₃. Its name comes from its main chemical components, fluorine and boron. It was first described in 1926.^[3]

Fluoborite's crystal system is hexagonal, meaning it has one six-fold axis of rotation. It also has a mirror plane perpendicular to the c-axis.^[5] Fluoborite is uniaxial, just like all other hexagonal minerals. Uniaxial means it has only one optic axis. It is anisotropic. Its relief is low, and it is birefringent.

There are three major settings fluoborite is found. It is found in skarns developed in metamorphosed boron-rich magnesium rocks, contact metamorphosed marble, and in contact metasomatic magnetite deposits. There are two major type localities for fluoborite. One is Tall Mine, Kallmora, Norberg, Västmanland, Sweden. It is an iron mine in a contact metasomatic magnetite deposit. The other type locality is the Huerta del Vinagre mine, Spain.^[6]

It occurs associated with ludwigite, chondrodite, magnetite and calcite in the Tallgruvan, Sweden occurrence. It occurs with mooreite, willemite, fluorite, hydrozincite, pyrochroite, zincite and rhodochrosite at Sterling Hill, New Jersey.^[2]

References