Jeremejevite

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.

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

Jeremejevite

General

Category Borate mineral

Formula Al6B5O15(F,OH)3

IMA symbol Jer

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

Etymology

The first colorless crystals were found in the pegmatite of Soktuj Gora in the Adun-Kholon Mountains near Nerchinsk in the Russian region of Transbaikalia and described in 1883 by the French mineralogist Augustin Alexis Damour, who named the mineral in honor of the Russian mineralogist, crystallographer and engineer Pavel Vladimirovich Eremeyev (1830–1899). 

The type material of the mineral is kept at the Mining Institute of Saint Petersburg, Russia, under catalog number 412/1. 

Since jeremejevite was already known and recognized as a separate mineral species long before the founding of the International Mineralogical Association (IMA), this was adopted by its Commission on New Minerals, Nomenclature and Classification (CNMNC) and referred to jeremejevite as a so-called grandfathered mineral. 

Classification

In the outdated 8th edition of the mineral classification according to Strunz, jeremejewite belonged to the common mineral class of “carbonates, nitrates and borates ” and there to the division of “island borates (nesoborates)”, where it was the only member of the unnamed subgroup Vc/A.01a within the “jeremejewite-kotoite group” (Vc/A.01).

In Stefan Weiß's Lapis Mineral Catalogue, which, out of consideration for private collectors and institutional collections, still follows this old form of Karl Hugo Strunz 's system, the mineral was given the system and mineral number V/G.05-30. In the "Lapis Systematics," this also corresponds to the "Island Borates" section, where jeremejewite, together with chubarovite, fluoborite, hydroxylborite, jacquesdietrichite, karlite, mengxianminite, and painite, forms an independent but unnamed group (as of 2018). 

The 9th edition of Strunz's mineral classification, valid since 2001 and updated by the IMA until 2009, classifies jeremejevite in the newly defined class of "borates" and within that in the division of "monoborates". This division is further subdivided according to the structure of the borate complex and the possible presence of additional anions, so that the mineral, according to its composition, can be found in the subdivision "BO 3 with additional anions; 1(Δ) + OH etc.", where it is the sole member of the unnamed group 6.AB.15.

The Dana mineral classification, like the old Strunz classification, classifies jeremejewite in the class of "carbonates, nitrates, and borates," but in the division of "anhydrous borates with hydroxyl or halogen." Here, it is the only member of the unnamed group 25.08.01 within the subdivision " anhydrous borates with hydroxyl or halogen."

Properties

Jeremejevite is a mineral that shows pleochroic properties, which is an optical phenomenon in which the mineral's color appears to change depending on the angle at which it is viewed. 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 also piezoelectric, meaning that it would generate electricity when under mechanical stress.

Crystal structure

Jeremejevite crystallizes hexagonally in the space group P 6 3 / m (space group no. 176) with the lattice parameters a = 8.56 Å and c = 8.18 Å and 2 formula units per unit cell. 

Morphology

Most of the intensely blue jeremejewites lack precise edges and crystal faces. Jeremejewite crystals can be up to approximately 6 cm long and approximately 5 mm thick, but can also have a needle-like shape with diameters of approximately 1 mm. Many crystals become somewhat narrower toward the top. Larger crystals still attached to the matrix are rare. The reason for this is still unknown.

Physical properties

Jeremejevite has piezoelectric properties, meaning that alternating elastic deformation builds up an electrical voltage in the crystal, just like in the well-known quartz. 

Mining and localities

Jeremejevite 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. It was first found in facetable form in Namibia, which were blue-green pyramidal crystals up to 2 cm (0.79 in). Later, there was a new source revealed in Namibia, near Usakos in 2001. Nowadays, most of the stones on the market are from that deposit.

Use as a gemstone

Jeremejevite crystals can be colorless, light yellowish-brown, or light to dark blue. Greenish and violet stones are also known. The rarest and most valuable color is a rich cornflower blue. Light or medium blue crystals are also highly sought after. Some colorless or light blue crystals gradually fade to a deeper blue near the bottom.

As with other gemstones, the value of a jeremejevite depends primarily on its clarity, color, and weight: The most valuable stones should be eye-clean or loupe-clean, have an intense cornflower blue color, and be large (> 1 carat). Jeremejevites are typically faceted in baguette or emerald cuts, but are also available in oval faceted cuts.

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.

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 jeremejevite is a relatively durable stone, it should not be cleaned using ultrasound cleaning or steaming; the stone usually contains liquid inclusions, which could shatter the stone if cleaned using these methods. It is recommended to clean them with warm water, a mild detergent, and a soft brush instead.

Synthetic

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.

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