Oxy-schorl

oxy-schorl

tourmaline

muscovite

garnet

Images

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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