Tephroite

Tephroite is a non-metallic manganese silicate mineral with the formula, Mn2SiO4, that is one of the unusual minerals found at the famous mines of Sterling Hill and Franklin, New Jersey, USA. It can also be found in England and Sweden.Tephroite has a hardness of 6 and a specific gravity of approximately 4.1, which is heavy for non-metallic minerals. Its name comes from the Greek tephros - "ash gray"- for its color. It can also be found olive-green, greenish-blue, pink or brown.
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(n.)
A silicate of manganese of an ash-gray color.
  

General Information:
 Chemical Formula:
Mn2SiO4
 Composition:
(Molecular Weight = 201.96 gm)
Manganese 54.41 % Mn
Silicon 13.91 % Si
Oxygen 31.69 % O 
 Empirical Formula:
Mn2+2(SiO4)
 Environment:
Contact metamorphism of manganese bearing rocks.
 Locality:
Franklin and Sparta, New Jersey, USA.
 Name Origin:
From the Greek tephros - "ash gray" for its color.
Physical Properties:
 Cleavage:
[010] Indistinct
 Color:
gray, olive green, bluish green, red, or reddish brown.
 Density:
4.11 - 4.39, Average = 4.25
 Diaphaniety:
Transparent to translucent
 Habits:
Massive - Granular - Common texture observed in granite and other igneous rock., Granular - Generally occurs as anhedral to subhedral crystals in matrix., Prismatic - Crystals Shaped like Slender Prisms (e.g. tourmaline).
 Hardness:
6.5 - Pyrite
 Luminescence:
None.
 Luster:
Vitreous - Greasy
 Streak:
gray
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