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Formula: Al16B6O30(Si2O7 )
Sorosilicate (Si2O7 groups), boron-bearing mineral
Crystal System: Monoclinic
Specific gravity: 3.07 calculated
Streak: White
Colour: Colourless
Environments
Pegmatites
Metamorphic environments
Boralsilite forms colourless prisms up to 2 mm long and 0.25 mm across and is commonly euhedral in cross
section. It is estimated to have formed between 600oC and 750oC and a pressure of 3 to 5 kbar
(AM 83.638-651).
Localities
There are two co-type localities, Stornes Peninsula, Larsemann Hills, Prydz Bay, Ingrid Christensen Coast, Princess
Elizabeth Land, Eastern Antarctica, and Almgjotheii, Flatestøl, Lund, Rogaland, Norway.
At Stornes Peninsula, Larsemann Hills, Prydz Bay, Ingrid Christensen Coast, Princess Elizabeth Land, Eastern
Antarctica, boralsilite is a high-temperature phase in
pegmatites cutting
granulite-facies
metapelitic rocks.
A stable assemblage is quartz -
K-feldspar - boralsilite -
schorl/dravite
(AM 83.638-651).
At Almgjotheii, Flatestøl, Lund, Rogaland, Norway, boralsilite occurs in the contact aureole of the intrusive
complex. Stable assemblages include
(1) K-feldspar - plagioclase
- boralsilite - werdingite -
dumortierite -
grandidierite
(2) quartz - K-feldspar -
boralsilite - dumortierite -
andalusite +/- sillimanite
The composition of the Almgjotheii material appears to result from solid solution of boralsilite with
sillimanite and subordinate
werdingite
(AM 83.638-651).
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