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Formula: ◻(Al2Li)Al6(Si6O18)(BO3)3(OH)3F
Cyclosilicate (ring silicate), tourmaline group
Crystal System: Trigonal
Specific gravity: 3.07 measured, 3.071 calculated
Hardness: 7
Streak: White
Colour: Light pink
Luminescence: No fluorescence under UV
Environments
Fluor-rossmanite is a new mineral, approved in 2024 (?) and to date (April 2025) reported only from the
type locality
Localities
At the type locality, the Krutaya pegmatite vein, Malkhan pegmatite field, Krasnyi Chikoy, Krasnochikoysky District,
Zabaykalsky Krai, Russia, the Malkhan field is unique in its extraordinary abundance of
pegmatite dykes containing semi-precious stones, primarily
gem-quality and collectible tourmaline. The Malkhan field contains
more than 300 pegmatites, 40 of which are
tourmaline-rich.
The Krutaya pegmatite, where fluor-rossmanite was found, is one of the oldest-known in the Malkhan field, being
discovered in 1981. Initial prospecting work in the mid-1980s, however, revealed poor
tourmaline mineralisation and crystal quality. Most of the body is
composed of graphic pegmatite, consisting of
K-feldspar, quartz and
albite. The central part of the
pegmatite contains orange
spessartine, muscovite,
beryl and tourmaline in
addition to individual miaroles, up to 0.3 × 0.2 m in size, lined with quartz
crystals. In 2020 work was resumed on the pegmatite, but only
very few crystals of gem-quality tourmaline were uncovered, one of
which contained fluor-rossmanite.
Fluor-rossmanite is the fifth new mineral discovered at the Malkhan pegmatite field; the others are
bismutocolumbite,
borocookeite,
oxybismutomicrolite and
nioboixiolite-(Mn2+).
Fluor-rossmanite occurs as an intermediate light pink zone up to 3 mm thick in a chemically heterogeneous,
concentrically zoned, polychrome tourmaline crystal 3.2 × 2 cm in
size. This crystal is unique in terms of the number of
tourmaline group species it contains, at least eight. Its
dark brown core consists of unusually manganese-rich
fluor-tsilaisite;
princivalleite and a potentially new
tourmaline species, a Mn2+-F-analogue of
foitite, are also recorded in this zone. The greenish-yellow intermediate
zone consists of manganese-rich
fluor-elbaite. Very few analyses of this zone correspond to
darrellhenryite. This zone is surrounded by a
manganese-poor, light pink zone composed mainly of fluor-rossmanite.
The zone also includes rossmanite and its oxy-analogue, another potentially
new tourmaline species. Finally, the yellowish-green peripheral zone
consists of late-generation, manganese-bearing
fluor-elbaite. From the centre of the dark brown zone to the edge of the
crystal, the Mn content decreases and the (Li+Al) content increases up to the middle of the pink zone where MnO reaches
0.21 wt%. Subsequently, this compositional trend is reversed from the centre of the pink zone to the edge of the crystal
(MM 88.668–676).
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