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Formula: (Mg,Al,Fe)6Al4(Si,Al)4(B,Si,Al)(O,OH,F)22
Sorosilicate (Si2O7 groups), boron-bearing mineral,
forms a series with kornerupine
Crystal system: Orthorhombic
Specific gravity: 3.341 to 3.345 measured
Hardness: 6½ to 7
Colour: Grey-green, gold-brown, purplish grey, grey
Environments
Localities
At the type locality, the Granulite outcrop, Waldheim, Mittelsachsen, Saxony, Germany, unterminated prismatic
crystals of prismatine up to about 6 cm in length occur, distributed randomly or radially grouped. They
occur in a granulite facies environment associated
with garnet, oligoclase,
phlogopite, sapphirine,
sillimanite and tourmaline
(Mindat).
Prismatine from Waldheim - Image
At the Eastern Ghats, Andhra Pradesh, India, fluorine-rich prismatine and
hercynite are major constituents of a Fe-Al-B-rich lens in
ultrahigh-temperature granulite facies
quartz - sillimanite -
hypersthene/a> - cordierite
gneisses. Sapphirine,
magnetite, biotite and
sillimanite are subordinate
(MM 67.5.1081–1098).
At the Sondalo granulites, Sondrio Province, Lombardy, Italy, prismatine has been found. The
granulite consists of
albite-rich plagioclase +
cordierite + sillimanite +
rutile + hercynite +
corundum + quartz and is
interpreted as a restite (residual material) formed after partial melting of
amphibolite facies
tourmaline-bearing metasediments at about 900°C and 0.8 GPa.
Prismatine grains, which form a coarse aggregate with tourmaline,
biotite and albitic
plagioclase, have inclusions of
sapphirine, hercynite and
corundum
(EJM 15.2.393–400).
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