Helvite

(n.)
A mineral of a yellowish color, consisting chiefly of silica, glucina, manganese, and iron, with a little sulphur.
  

General Information:
 Chemical Formula:
Mn4Be3(SiO4)3S
 Composition:
(Molecular Weight = 555.10 gm)
Manganese 39.59 % Mn
Beryllium 4.87 % Be
Silicon 15.18 % Si
Sulfur 5.78 % S 
Oxygen 34.59 % O 
 Empirical Formula:
Mn1+4Be3(SiO4)3S
 Environment:
Found in skarns, pegmatites, and hydrothermally altered rocks.
 Locality:
Schwarzenberg and Breitenbrunn, Germany.
 Name Origin:
From the Greek helios - "sun."
Physical Properties:
 Cleavage:
[111] Indistinct, [111] Indistinct, [111] Indistinct
 Color:
brown, brownish yellow, gray, yellow, or yellow green.
 Density:
3.16 - 3.36, Average = 3.26
 Diaphaniety:
Translucent to opaque
 Habits:
Massive - Uniformly indistinguishable crystals forming large masses., ,
 Hardness:
6-6.5 - Orthoclase-Pyrite
 Luminescence:
None.
 Luster:
Vitreous - Resinous
 Streak:
grayish white
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