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Formula: Mn2+Sn(BO3)2
Anhydrous monoborate,
manganese-bearing mineral
Crystal System: Trigonal
Specific gravity: 4.73 measured, 4.85 calculated
Hardness: 5 to 6
Colour: Colourless, yellow-brown, honey-yellow
Luminescence: No cathodoluminescence or UV luminescence
Environments
Pegmatites
Hydrothermal environments
Tusionite is of late-stage hydrothermal origin, rare in granite
pegmatites, typically in miarolitic cavities
(HOM).
Localities
At the Řečice pegmatite, Řečice, Žďár nad Sázavou District, Vysočina Region, Czech Republic, tusionite is
associated with tourmaline,
hambergite, danburite,
hellandite, boromuscovite
and cassiterite
(HOM).
Tusionite from the Řečice Pegmatite -
Image
At the type locality, the Tusion River Valley, Gorno-Badakhshan, Tajikistan, tusionite occurs as lamellar
intergrowths up to 1.5 cm in size with tetrawickmanite, and as small
tabular crystals in miarolitic cavities associated with tourmaline,
danburite, hambergite,
quartz, orthoclase and
albite, in granite
pegmatites. The
pegmatites cut Precambrian (more than 539 million years ago)
garnet-biotite
gneiss. The tusionite is yellow-brown to colourless with a
vitreous lustre
(AM 69.1193).
At the Columbia Mine, Thomas Mountain, Thomas Mountain [town], Cahuilla Mining District, Riverside County,
California, USA, new (in 1994) localities of tusionite were found in the
granitic
pegmatites Belo Horizonte No. 1 and New Columbia No. 1. The
occurrences are in boron-rich complex
pegmatites of the
elbaite subtype, characterised by the presence of common
tourmaline and other boron-rich
minerals such as hambergite,
danburite, hellandite and
boromuscovite.
Tusionite occurs as thin blades and fan-like rosettes up to 3 cm across enclosed in massive
pegmatite, or as small tabular crystals in miarolitic
pockets. It is associated with K-feldspar,
albite, quartz and
tourmaline. Tusionite aggregates from massive
pegmatite are commonly replaced by fine-grained
cassiterite
(CM 32.903-907).
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