Berborite

Berborite is a beryllium borate mineral with the chemical formula Be₂(BO₃)(OH,F)·(H₂O). It is colorless and leaves a white streak. Its crystals are hexagonal to pyramidal. It is transparent and has vitreous luster. It is not radioactive. Berborite is rated 3 on the Mohs Scale.[3]

Berborite
Berborite on natrolite
General
Category	Borate minerals
Formula (repeating unit)	Be2(BO3)(OH,F)•H2O
IMA symbol	Bbo[1]
Strunz classification	6.AB.10
Dana classification	26.1.1.1
Crystal system	1T polytype: Trigonal 2H polytype: Hexagonal 2T polytype: Trigonal
Crystal class	1T polytype: Pyramidal (3) 2H polytype: Pyramidal (6) 2T polytype: Ditrigonal pyramidal (3m)
Space group	1T polytype: P3 (no. 143) 2H polytype: P63 (no. 173) 2T polytype: P3c1 (no. 158)
Unit cell	a = 4.43 Å, c = 5.34 Å; Z = 2; V = 90.76 Å3 (2H polytype)
Identification
Color	Colorless
Twinning	Complex
Cleavage	{0001} Perfect
Fracture	Uneven - Flat surfaces (not cleavage) fractured in an uneven pattern.
Mohs scale hardness	3
Luster	Vitreous (Glassy)
Streak	white
Diaphaneity	Transparent
Density	2.2
Optical properties	Uniaxial (-)
Refractive index	nω = 1.580 nε = 1.485
Birefringence	δ = 0.095
Ultraviolet fluorescence	none
References	[2][3][4][5]

Berborite occurs in 1T, 2T, 2H polytypes.[4]

It was first described in 1967 for an occurrence in the Lupikko Mine, Ladoga Region Karelia Republic, Russia. It has also been reported from Tvedalen, Larvik, Vestfold, and Siktesøya Island, Langesundsfjord, Porsgrunn, Telemark, Norway.[2][4] It occurs in serpentine altered dolomite in association with skarn enriched in tungsten, strontium, beryllium and boron in the Karelia occurrence and in vugs with natrolite and thomsonite in Norway.[3][4]