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Formula: Al6(BO3)5F3
Anhydrous borate containing halogen
Crystal System: Hexagonal
Specific gravity: 3.28 measured, 3.27 calculated
Hardness: 7
Streak: White
Colour: Colourless, light yellow brown, aquamarine blue; colourless in transmitted light
Luminescence: Not fluorescent under UV
Electrical properties: Piezoelectric
Environments
Pegmatites
Hydrothermal environments
Jeremejevite is a rare late hydrothermal mineral formed in
granitic
pegmatites
(HOM).
Localities
At Wannenköpfe Quarry, Ochtendung, Maifeld, Mayen-Koblenz, Rhineland-Palatinate, Germany, jeremejevite occurs
in xenoliths in trachytic
pumice tuff exposed in a
quarry. Associated minerals include biotite,
cordierite, corundum,
enstatite, nepheline,
osumilite, pseudobrookite,
sanidine and topaz.
The jeremejevite often occurs as tiny blue to pale yellow crystals or clusters of crystals, typically on
highly vitreous sanidine
(R&M 98.2.160-170).
At Emmelberg, Üdersdorf, Daun, Vulkaneifel, Rhineland-Palatinate, Germany, in old quarry on Emmelberg Mountain,
there are exposed rocks comprising lavas and
olivine-nepheline-rich dikes.
The lavas are primarily mafic alkali in composition comprising
nephelinites,
melilitites and
leucites. The lava has vesicles and xenoliths that contain the
mineralisation.
The jeremejevite commonly occurs as sprays of blue hexagonal crystals less than 1 mm in size with pyramidal
terminations. Some of the yellow crystals that were originally visually identified as jeremejevite were
analysed and found to be mullite
(R&M 98.2.160-170).
At Niveligsberg, Drees, Kelberg, Vulkaneifel District, Rhineland-Palatinate, Germany, at Niveligsberg Mountain a
quarry in alkali basalt hosts xenoliths that contain
jeremejevite associated with sanidine and
topaz
(R&M 98.2.160-170).
At the Mogok Stone Tract, Myanmar, in 2005 jeremejevite crystals measuring up to 4 cm were obtained from
alluvial deposits and pegmatites. The pale yellow crystals
were sold originally as either quartz or
beryl, but later analyses showed them to be jeremejevite. The crystals
are typically prismatic and some of them yielded faceted yellow stones, up to 4.35 carats.
Pegmatite-hosted jeremejevite is found at Pan-Taw,
Kyauk-sin and Sakhan-gyi in the Mogok Stone Tract. Typical hexagonal crystals to 4 cm originate from alluvium and
pegmatite on Loi-sau Mountain, located 19 kilometers
northeast of Mogok, with some associated quartz and pink
tourmaline. During the late 2000s, jeremejevite crystals equal
in size and of similar pale-yellow/amber came from the Pantahole mine, Loi-sau Mountain, Mogok Township, Mandalay
region in Myanmar
(R&M 98.2.160-170).
At Mile 72, Cape Cross area, Arandis Constituency, Erongo Region, Namibia, the first find in the
pegmatites produced some of the finest jeremejevite
known, being gemmy electric blue crystals up to 7 cm in length. Later loose, dull, pale yellow jeremejevite
crystals, some to 5 cm in size, were found
(R&M 98.2.160-170).
Associated minerals include albite,
tourmaline, quartz and
gypsum
(HOM).
At the Erongo Mountains, Karibib Constituency, Erongo Region, Namibia, jeremejevite has been found as
colourless, pale yellow to pale blue crystals from small miarolitic cavities in the Erongo
granite. Most were loose, small (1–1.5-cm) crystals, although some
were up to 8 cm, and one extraordinary crystal measured 16.7 cm in length. The colour varies from light blue to
dark blue to colourless, and some crystals are colour-zoned.
In February 2010 a second discovery of over 1,000 jeremejevite crystals was again made here. This time, the
crystals, although an attractive and often intense blue, were highly corroded and etched. Unlike the previous finds,
these etched crystals are partly encased in hollow, highly corroded, leached “tubes” of matted, acicular
tourmaline that was analysed as
foitite. These hollows appear to delineate the original, unaltered
jeremejevite crystals, and some are partially filled by calcareous
clay. The largest hollows are up to 15 cm long and 3 cm wide, suggesting
this was the size of the once enclosed and now absent jeremejevite. Associated minerals include
foitite, smoky quartz,
schorl and topaz
(R&M 98.2.160-170).
The occurrence of tourmaline overgrowing jeremejevite in the
pegmatites gives rise to the assumption that
jeremejevite might act as a precursor for tourmaline formation
(EJM 29.239-255).
At the type locality, Soktuj Gora, Adun-Cholon Range, Nerchinsky District, Zabaykalsky Krai, Russia, crystals
of jeremejevite occur up to 10 cm in length, and are typically pale yellow to pale brown and transparent to
translucent. Jeremejevite occurs here as a late-stage hydrothermal mineral in
granitic
pegmatites. Museum specimens consist of transparent, pale
yellow 3 to 4 cm hexagonal crystals
(R&M 98.2.160-170).
Sri Lanka has also produced jeremejevite, and although the supply might be very limited, one of the largest
known faceted stones comes from this country. This is a very pale blue 106.5 carat gem jeremejevite cut from
a rough waterworn nodule weighing 254 carats. The exact locality of this gemstone is not given, but the Ratnapura
area in Sri Lanka is known to produce colourless jeremejevite
(R&M 98.2.160-170).
The Rangkul' pegmatite field, Rangkul' Highlands, Gorno-Badakhshan, Tajikistan contains peraluminous
granitic
pegmatites that host various gemstones including
tourmaline, topaz,
hambergite and jeremejevite. The Fantaziya
pegmatite, in particular, has yielded gem-quality light
yellow jeremejevite, some of which has been faceted to yield gemstones less than 1 carat. The Fantaziya
pegmatite occurs as a 10-meter-long, 3-meter-wide
lenticular body hosted in marble. Cavities to 1.5m3 contain
the gemstones together with fluorite,
quartz, albite and
schorl. Another locality within Gorno-Badakhshan is a
granitic
pegmatite from the Vez-Dara River valley that to-date has
produced a single 6-mm pale yellow, transparent jeremejevite crystal
(R&M 98.2.160-170).
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