Talmessite

General Information:
 Chemical Formula:
Ca2Mg(AsO4)2·2(H2O)
 Composition:
(Molecular Weight = 418.33 gm)
Calcium 19.16 % Ca
Magnesium 5.81 % Mg
Arsenic 35.82 % As
Hydrogen 0.96 % H 
Oxygen 38.25 % O 
 Empirical Formula:
Ca2Mg(AsO4)2·2(H2O)
 IMA Status:
Approved IMA 1960
Physical Properties:
 Color:
colorless, white, or light green.
 Density:
3.2 - 3.5, Average = 3.35
 Diaphaniety:
Transparent to Translucent
 Hardness:
5 - Apatite
 Luster:
Vitreous (Glassy)
 Streak:
white
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