Rarest Gemstones: Jeremejevite

IMG_7987-1.JPG

Jeremejevite, one of the rarest gemological materials, was named after Russian mineralogist P. W. Jeremejev in 1883, but there are rarely any specimens found in Russia today. Recently Namibia has started to produce some mentionable crystals, but in such small amounts the stone is still very rare. Jeremejevite is typically found in pale blue-green, cornflower-blue to yellowish bown hues.

JEREMEJEVITE CLASSIFICATION
Common Name: Jeremejevite
Species: Jeremejevite
Colors: blue-green, cornflower blue, brown, pale yellow and colorless

Key Separations: RI, birefringence and possible optic character.

JEREMEJEVITE PROPERTIES
Chemical Name: aluminum borate fluoride hydroxide
Chemical Formula: Al6B5O15(F,OH)3
Crystal System: Hexagonal
Classification: Borate
Crystallinity: Crystalline
Transparency: Transparent
Refractive Index: 1.64-1.651 Tolerance: (+0.002/-0.001)
Birefringence: 0.009
Optic Character: uniaxial and biaxial
Optic Sign: negative
Polariscope Reaction: doubly refractive (DR)
Fluorescence: SWUV: Inert, LWUV: Inert
Hardness: 6.5-7.5
Streak: white
Specific Gravity: 3.27-3.31
Toughness: Poor
Luster: Vitreous
Fracture: Conchoidal
Cleavage: None

Jeremejevite was first described in 1883 by French mineralogist Augustin Alexis Damour, who named it in honour of the Russian mineralogist and engineer Pavel Wladimirowich Jeremejev. Only a few localities of this rare borate mineral are known worldwide. Jeremejevite was discovered in 1883 at Mt Soktuj, Eastern Siberia, Russia. Only a few isolated crystals up to 5 cm in length have been reported from the type locality. The crystals resembled a yellowish beryl in appearance. For more than 100 years, this mineral was one of the rarest of all known minerals.

In 1973 a second occurrence of jeremejevite was found at a small pegmatite mine known as “Mile 72” north of Swakopmund, Namibia. The mine was exploited by the well-known mineral dealer Sid Pieters. Only a few crystals were found, which showed a fine blue colour. In 1976 a pocket was hit that produced about 100 of the finest known crystals of blue jeremejevite measuring up to 5 cm in length and 0,5 cm in diameter. Very few crystals on matrix were found.

Since this find, jeremejevite became a highly sought-after mineral by collectors worldwide. The only other known localities are the Ameib Farm Erongo Mountains, Namibia; Eifel Mountains, Germany; Sagaing District, Burma (Myanmar); and the Pamir Mountains, Tajikistan. The latter find is not well documented. About 10 yellow to brown crystals of little transparency up to 5 cm in length are reported from this locality.

The Mile 72 Namibian occurrence is in a wind-blown flat surface of hard, ocean-weathered granite protruding from a sandy stretch of beach about 750 m back from the shoreline, where the breakers lap the Namib Desert. It is close to milepost 72; that is, 72 miles by road north of Swakopmund.

The initial discovery was made by a woman known as “Tannie Klippie”, who was the wife of John Marais. Mr Marais was employed by the state as a road-grader operator, and his wife frequently spent her days walking behind her husband’s grader collecting pretty rocks. In 1973 the road leading to the Mile 72 fishing camp road was angled at approximately 45 degrees southward to the coast road from its current location. Mr Marais’ grader turned over a few jeremejevite crystals that had weathered out into the sand, and Tannie Klippie was there to pick them up. These specimens eventually made their way to the sharp eye of Windhoek gem and mineral dealer Sid Pieters. At first glance Pieters thought them to be aquamarine but an analysis identified them as jeremejevite. This was confirmed by an analysis of a cut gem performed by Richard T. Liddicoat of the Gemological Institute of America (1973) .

Mr Pieters quickly filed three 300 x 600 m claims where Tannie Klippie stumbled over the crystals. Peter Kitler did the actual mining and the tourmaline miner, Jan Coetzee, from Usakos did the blasting. They decided to open cut the granite, beginning on the eastern end and drive a trench westward perpendicular to the vertical vein containing the jeremejevite pockets. The first pocket found was in the altered granite. It yielded a number of gemmy but colourless crystals to 7,6 cm. The trench was continued through 5-6 m of hard granite, maintaining a depth of 1,5 m. This work netted just a meagre handful of loose, colourless crystals from small pockets along the vein.

In mid-1998, Brian Lees of Collector’s Edge Minerals teamed up with C. J. Johnston, an American mining geologist and mineral dealer based in Omaruru, to form Khan River Mining (Pty) Ltd. Their intention was to excavate further along the pegmatite veins in the hope of finding more jeremejevite. The mining commenced in early January 1999 and upon cleaning out the “Kitler pit” the first truly mechanized mining effort at Mile 72 commenced. In spite of a difficult mining environment 2 700 tons of rock were removed within the first six months. With the advantage of having heavy equipment more rock was mined in the first two weeks than the entire Sid Pieters effort from 1973 to 1976. Within the first three weeks, directly below the area where the best material had been found in 1973, a coarse-grained granitic pegmatite was encountered which produced approximately 300 single, colourless to pale yellow water-clear jeremejevite crystals up to 5 cm and only one pale blue crystal. Over the next 12 months an additional 14 target areas were identified and an estimated 2 300 tons of rock mined. In addition to these targets 15 trenches were excavated. While the effort produced some interesting specimens of feldspar, apatite, quartz and schorl, no further jeremejevites were found. Namibia is one of the very few countries in the world that constitutionally guarantees the protection of the environment. Consequently it is highly unlikely that any further mining will take place at Mile 72.

In March 2001, pegmatites containing jeremejevite were discovered near the summit of an isolated inselberg on Farm Ameib near the border with the farm Davib-ost, halfway between the village of Tubussis and the town of Usakos on the south side of the Erongo Mountains. As with the Mile 72 crystals, the first intense blue crystals found were thought to be aquamarines, and caused little excitement. A few thousand crystals have since been recovered. These workings are restricted to a 100 m2 area on a steeply sloping surface near the top of the inselberg. The mining in the Erongo Mountains is a simple brute force manual labour affair. The diggers must first walk 14 kilometres from the Government gravel road to reach the base of the mountain. It is then a very hard climb of nearly 500m to reach the top. There is no water, so miners must carry their own supply together with their modest equipment. The majority of the diggers, who have numbered up to 150, have nothing more than a hammer, chisel and shovel with which to attack the granite. Some of the excavations now exceed 6 m in depth. The majority of the Erongo Mountain jeremejevite crystals are under 2,5 cm in size, but a respectable number of larger crystals, over 200, range up to 5 cm in length and 1 cm wide. There have been unverified reports of crystals in excess of 8 cm.

You might also read this article by Kenneth Scarratt, Donna Beaton and Garry Du Toit on Gems&Gemology

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s