Mineral of the Month - Jeremejevite

Posted by Site Moderator Webmaster on Wednesday, September 28, 2011 Under: Mineral of the Month

Crystal system: Hexagonal Hardness: 6,5 – 7,5

Density: 3,28 – 3,31 Streak: White

Colour: Colourless, white, yellowish, pale to dark blue

Cleavage: None

Occurrence: A rare late hydrothermal mineral formed in granitic pegmatites.

Habitat: Crystals are typically hexagonal prismatic, may be tapered with pyramidal termination.

Composition: Borate Al₆B₅O₁₅(F,OH)₃

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 – with various spelling - (1830–1899). 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.

But 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. Actually, more artificially mounted specimens exist where crystals of jeremejevite are glued onto feldspar.

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.

I also stumbled upon two articles which reported that jeremejevite was also found in Madagascar in 2004. Apparently the largest faceted jeremejevite in existence, weighing a whopping 59,68 carats, was cut from material from this find. Mention is also made of a cut stone weighing 12,78 carats with inclusions of hollow tubes that appear to have iron staining. To me it just looks like normal white quartz with rutile inclusions. None of the other localities has jeremejevites with inclusions.

Reference is also made in The Mineralogical Record of a 7,88 carat faceted stone that was purchased in Madagascar as a colourless “achroite” tourmaline and is apparently the only jeremejevite sample reliably known from Madagascar. The locality of the Madagascar mine is not divulged. This all together sounds a bit suspicious, so if any club member has more knowledge about the Madagascar jeremejevite or wants to do more research, you are more than welcome to do so and inform us about your findings. While you are at it, what is the reason for the different colours in jeremejevite - possibly defects in the structure or trace elements? Why are only colourless or pale blue crystals terminated?

In total it would, therefore, appear that there are only 12 diggings/mines worldwide where this rare mineral was ever found, of which many are now defunct. Duncan Miller also mentioned in a previous Mineral of the Month article on this mineral that crystals have also been reported from Vietnam. Anyway, back on local soil; Namibia still has the best colour and quality jeremejevite specimens in the world in my opinion. The Mile 72 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.

A small, narrow, vertical zone of grey to black, medium-grained quartzite was found to intersect the main vein at about 90 degrees. Here, at the junction of the veins, is the only place where blue jeremejevite crystals were found. Associations included albite, quartz, lepidolite, apatite, schorl, tourmaline and gypsum. It is not known why the crystals at this specific intersection were blue instead of colourless. The largest pockets containing the best blue crystals were found within a metre of the vein intersection. These pockets were 10 cm across. Later mining efforts followed the vein system to a depth of 3 m, showing the dyke itself to be consistently at least 20 cm in width over that distance. Only a few colourless crystals of smaller size and lower quality were found as a result. Mining was therefore halted.

In December 1974, Duncan Miller had the privilege of being flown to Windhoek, along with his faceting machine, to cut twenty of these crystals. That Christmas Sid had him and an assistant literally crawling over the prospect to recover fragments of this rare mineral. As a reward he was allowed to keep some light blue and colourless specimens, two of which he has faceted. Duncan, what can we say, it must have been a very awful and boring job to do, but hey somebody had to do it!!

Jeremejevite specimens from the original find at Mile 72, Cape Cross, Namibia.

The two cut stones, 0,07 and 0,14 ct, were faceted by Duncan Miller. Specimens and photo by Duncan Miller.

According to Herting and Strunz, a second discovery approximately 100 m to the east was made in August 1976, when careful drilling and blasting yielded approximately 100 well-formed blue crystals up to 5 cm. However, according to Mr Kitler and Mr Coetzee, this pocket contained only relict, heavily altered crystals. Approximately only 100 tons of rock was removed during the whole mining process.

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.

During 2010 etched jeremejevites were discovered at Erongo. Some of them are imbedded in a green tourmaline matrix or in some cases, almost surrounded by a green tourmaline cast. The tourmaline comprises very small crystals and is possibly a new tourmaline group which is being researched at the moment. The jeremejevites were also big, some were up to 5 cm long and of the same dark blue colour as those discovered at Cape Cross. They were a big hit at this year’s 2011 Tucson show. Article - JdJ