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Formula: Na(Al2Li)Al6(Si6O18)(BO3)3(OH)3O
Cyclosilicate (ring silicate), borosilicate,
tourmaline group,
lithium-bearing mineral
Crystal System: Trigonal
Specific gravity: 3.03 measured, 3.038 calculated
Hardness: 7
Streak: Pinkish white
Colour: Intense to pale pink
Luminescence: No fluorescence under UV
Solubility:
Common impurities:
Environments
Darrellhenryite is a relatively new mineral found in lithium-rich
pegmatites and approved in 2012.
Localities
At the type locality, the Nová Ves pegmatite, Nová Ves, Český Krumlov District, South Bohemian Region, Czech Republic,
darrellhenryite was discovered in a complex lithium-bearing
pegmatite. The
pegmatite occurs as a symmetrically zoned dike, up to 8 m thick and
about 100 m long, that cuts a serpentinite body which is enclosed in
leucocratic (having more light coloured minerals than dark ones) granulites.
From the contact inward, it consists of
(1) an outermost granitic unit with biotite,
(2) a coarse-grained albite unit locally with graphic intergrowths of
K-feldspar + quartz and aggregates of
muscovite + quartz + tourmaline,
(3) blocky K-feldspar and blocky petalite,
and
(4) an albite-lepidolite unit,
the latter three units also containing lithium-bearing
tourmalines.
The lithium-bearing primary
minerals in the pegmatite are:
petalite > lepidolite
(trilithionite > polylithionite) >
lithium-bearing tourmalines
(darrellhenryite > fluor-elbaite) >
amblygonite. Secondary
spodumene + quartz aggregates after
petalite and secondary
montebrasite after primary
amblygonite are also present. Accessory
almandine-spessartine,
fluorapatite, beryl,
zircon, pollucite,
cassiterite, columbite and
microlite-group minerals
(fluornatromicrolite to
fluorcalciomicrolite) were also found in the
pegmatite. The
pegmatite may be classified as a complex
lithium-type, petalite-subtype but with
substantial amounts of lepidolite,
lithium-bearing tourmalines and
amblygonite.
Darrellhenryite (holotype) forms subhedral, short, columnar crystals and parallel aggregates, up to 3 cm long and up to
2 cm thick, which occur exclusively in the cleavelandite-rich portions of the
albite-lepidolite unit in the central part of
the dike. The associated minerals also include minor quartz, relics of pale brown,
blocky K-feldspar and colourless blocky
petalite, rare colourless flakes of
polylithionite and locally rare altered
pollucite. Very rare inclusions of late
muscovite, visible only in BSE images, occur within the aggregates of
darrellhenryite
(AM 98.1886-1892).
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