Eckermannite

General Information:
 Chemical Formula:
NaNa2(Mg4Al)Si8O22(OH)2
 Composition:
(Molecular Weight = 803.86 gm)
Sodium 8.58 % Na
Magnesium 12.09 % Mg
Aluminum 3.36 % Al
Silicon 27.95 % Si
Hydrogen 0.25 % H 
Oxygen 47.77 % O 
 Empirical Formula:
Na3Mg4Al(Si8O22)(OH)2
 IMA Status:
Approved IMA 1978
Physical Properties:
 Cleavage:
[110] Perfect
 Color:
blue green.
 Density:
3 - 3.17, Average = 3.08
 Diaphaniety:
Translucent
 Hardness:
5-6 - Between Apatite and Orthoclase
 Luster:
Vitreous (Glassy)
 Streak:
greenish white
More details...