Calciborite

Calciborite, CaB₂O₄, is a rare calcium borate mineral.

Calciborite
White crystals of calciborite from the type locality in Russia (Novofrolovskoye Deposit)
General
Category	Inoborates
Formula	CaB2O4
IMA symbol	Cbo[1]
Strunz classification	6.BC.10
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Pccn
Unit cell	a = 8.38 Å, b = 13.82 Å, c = 5.00 Å; Z = 8
Identification
Formula mass	125.70 g/mol
Color	White
Crystal habit	Prismatic crystals and radial clusters
Cleavage	None
Fracture	Conchoidal to uneven
Mohs scale hardness	3.5
Luster	Vitreous
Streak	White
Diaphaneity	Translucent
Specific gravity	2.878
Optical properties	Biaxial (-)
Refractive index	nα = 1.595 nβ = 1.654 nγ = 1.670
Birefringence	δ = 0.075
2V angle	Measured: 54°
References	[2][3][4][5]

It was first described in 1955 in the Novofrolovskoye copper–boron deposit, near Krasnoturinsk, Turinsk district, Northern Ural Mountains, Russia.^[4] It occurs in a skarn deposit formed in limestone adjacent to a quartz diorite intrusive. It occurs associated with: sibirskite (another rare calcium borate mineral), calcite, dolomite, garnet, magnetite and pyroxene.^[5] It has also been reported from the Fuka mine of Okayama Prefecture, Japan.^[4]