Celsian

Formula: Ba(Al2Si2O8)
Tectosilicate (framework silicate), feldspar group, dimorph of paracelsian
Specific gravity: 3.10 to 3.45
Hardness: 6 to 6½
Streak: White
Colour: Colourless, white, yellow

Metamorphic environments

Celsian occurs in amphibolite grade metamorphic rocks rich in manganese and barium.
It is associated with manganese-rich aegirine and biotite, paracelsian, jacobsite, hausmannite, rhodochrosite, rhodonite, rutile, hyalophane, baryte, cymrite, taramellite, quartz, zoisite, spessartine, dolomite and muscovite

At Broken Hill, New South Wales, Australia, celsian has been described from lenses and streaks in acid gneiss associated with plagioclase.
At the Benallt manganese mine at Rhiw, Wales, UK, celsian and paracelsian occur in a band in shale and sandstone associated with beds of manganese ore.

Common impurities: Fe,Mg,Ca,Na,K,F