Tenacity
-
-
Solubility
-
-
Durability
-
-
Specific Gravity
2.50-2.805.2
1
7.18
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Fracture
-
Subconchoidal, Conchoidal
Cleavage
Perfect
Good in one direction
Mohs Hardness
5-6.56-6.5
2
10
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Chemical Composition
Na 4(Al,Si) 12O 24Cl to Ca 4(Si,Al) 12O 24(CO 3,SO 4)Arthur Thomas , Gemstones (2009)
(Fe,Mn)Ta 2O 6Walter Schumann , Gemstones of the world (2001) More from other references