Darrellhenryite

darrellhenryite

lepidolite

petalite

polylithionite

Images

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

Pegmatites

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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