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Formula: Na(Fe2+2Al)Al6(Si6O18)(BO3)3(OH)3O
Cyclosilicate (ring silicate), borosilicate,
tourmaline group
Crystal System: Trigonal
Specific gravity: The measured and calculated values are 3.17 and 3.208 at Zlatá Idka and 3.19 and 3.198 at Přibyslavice
Hardness: 7
Colour: Greenish black, brownish black
Environments
Pegmatites
Metamorphic environments
Localities
McArthur River Mine, Athabasca Basin, Saskatchewan, Canada. The P2 fault is a 13 km-long steeply dipping reverse fault.
Three types of tourmaline have been observed in the metasedimentary basement rocks along the fault: early
oxy-schorl of metamorphic origin, hydrothermal oxy-dravite and
magnesio-foitite. Oxy-schorl formed in
granitic
pegmatites during peak metamorphism;
oxy-dravite formed from hydrothermal fluids after the peak metamorphism
and magnesio-foitite is a product of later, low-temperature
hydrothermal activity
(CM 54.661-679).
There are two co-type localities, Přibyslavice, Vlkaneč, Kutná Hora District, Central Bohemian Region, Czech Republic,
and
Zlatá Idka, Košice-okolie District, Košice Region, Slovakia.
In Zlatá Idka, Slovakia, fan-shaped aggregates of greenish black acicular crystals ranging up to 2 cm in size, forming
aggregates up to 3.5 cm thick were found in extensively metasomatically altered
metarhyolite pyroclastics with
quartz
+ albite + muscovite.
In Přibyslavice, Czech Republic, abundant brownish black subhedral, columnar crystals of oxy-schorl, up to
1 cm in size,
arranged in thin layers, or irregular clusters up to 5 cm across, occur in a foliated
muscovite-tourmaline
orthogneiss associated with
K-feldspar + albite +
quartz + muscovite +
biotite + garnet
(AM 98.485-492).
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