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
Unit cell	a = 8.5591(3), c = 8.1814(6) [Å]; Z = 2
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 , Russian mineralogist, engineer and professor, who collected the first specimens. (Jeremejev, German) (1830–1899).^[4]

Properties[]

Jeremejevite is a mineral which shows pleochroic properties, which is an optical phenomenon meaning the color of the mineral appears as if it changes colors depending on the axis it is viewed on. Blue specimens from Namibia show a light cornflower blue to colorless to light yellow pleochroism, while yellow materials show light yellow to colorless pleochroism. This mineral is piezoelectric, meaning that if it's under mechanical stress, it generates electricity.^[7]

Mining and localities[]

It occurs as a late hydrothermal phase in granitic pegmatites in association with albite, tourmaline, quartz and rarely gypsum. It has also been reported in the Pamir Mountains of Tajikistan, Namibia and in micro-crystalline form at the Eifel district, Germany.^[4] It was first found in facetable form in Namibia, which were blue-green pyramidal crystals up to 2 cm. Later, there was a new source revealed in Namibia, near Usakos in 2001.^[7] Nowadays, most of the stones on the market are from that deposit.^[5]

Jewelry industry[]

As an OH-end member, scientists have been able to synthesize jeremejevite, but only in micro-crystalline form, without fluorine. This synthesized variant of the mineral has no use in the jewelry industry.

Typically, faceted gems can reach up to 5 carats, but usually they range between less than 1 carat and 2 carats. However, new sources produced much larger faceted stones, the biggest faceted gem weighing 254 carats. This gem was found in Sri Lanka in 1990.

Even though jeremejevites are relatively durable stones, they shouldn't be cleaned using ultrasound cleaning or steaming in any way. It usually contains liquid inclusions, which could shatter the stone if it's being cleaned that way. It is recommended to clean them with warm water, a mild detergent, and a soft brush instead.^[7]

Due to its high value and rarity, it is considered a collectors' stone, who purchase it in mineral form, hence only a few specimens had been faceted so far.^[5]

Blue jeremejevite in rare, clear crystal form. Image width: 1.5 mm.

References[]

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