Jeremejevite

Jeremejevite
General
Category	Borate mineral
Formula (repeating unit)	Al6B5O15(F,OH)3
IMA symbol	Jer[1]
Strunz classification	6.AB.15
Crystal system	Hexagonal
Crystal class	Dipyramidal class (6/m) H-M symbol: (6/m)
Space group	P63/m
Identification
Color	Colorless, white, yellowish, blue, light yellow brown, aquamarine blue, rarely violet; colourless in transmitted light
Crystal habit	Prismatic
Cleavage	None observed
Fracture	Conchoidal
Mohs scale hardness	6.5 – 7.5
Luster	Vitreous
Streak	White
Diaphaneity	Transparent
Specific gravity	3.28 – 3.31
Optical properties	Uniaxial (-)
Refractive index	nω = 1.653 nε = 1.640
Birefringence	0.0130
Pleochroism	Colorless – light blue-violet
Other characteristics	Piezoelectric
References	[2][3][4]

Jeremejevite is an aluminium borate mineral with variable fluoride and hydroxide ions. Its chemical formula is Al₆B₅O₁₅(F,OH)₃. It is considered as one of the rarest, thus one of the most expensive stones. For nearly a century, it was considered as one of the rarest gemstones in the world.^{[5][better source needed]}

It was first described in 1883^[6] as small, single crystals in loose granitic debris in Mt. Soktui, Nerschinsk district, Adun-Chilon Mountains, Siberia.^[7] It was named after Pavel Vladimirovich Eremeev, Russian mineralogist, engineer and professor, who collected the first specimens (Jeremejev, German; 1830–1899).^[4]