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The Mineral tephroite

Tephroite & Zincite with Franklinite

Tephroite is uncommon member of the Olivine group. It is the manganese counterpart of Forsterite, and forms a series with Forsterite. Tephroite gets it name from the Greek word "tephros", meaning ash-colored, referring to its ash-gray color habit.

Chemical Formula

Mn2SiO4

Color

Gray, grayish-green, olive-green, brown, reddish-brown, pink

Crystal System

Orthorhombic

Properties

Streak
Light gray
Hardness
6
Transparency
Translucent. Rarely transparent.
Specific Gravity
4.0 - 4.1
Luster
Vitreous, greasy, waxy
Cleavage
2,1 ; 3,1- forming a 90º angle
Fracture
Conchoidal to uneven
Tenacity
Brittle

Crystal Habits

As rounded and fractured crystals, usually short and prismatic, but occasionally elongated. Also occurs grainy, massive, and in large cleavage fragments.

Additional Information

Composition
Manganese silicate, sometimes with some magnesium and zinc. Forms a series with Forsterite.
In Group
Silicates; Nesosilicates
Striking Features
Cleavage angles, color, and hardness.
Environment
In manganese-rich metamorphic deposits.
Rock Type
Metamorphic

Noteworthy Localities

Worldwide localities for Tephroite include Broken Hill, New South Wales, Australia; the Wessels Mine, Hotazel, Kalahari manganese fields, South Africa; and Langban, Sweden. In the U.S., the most well-known Tephroite is from Franklin, Ogdensburg, and Sparta, all in Sussex Co., New Jersey. Tephroite is also found in the Jail Hill Quarry, Haddam, Middlesex Co., Connecticut.

Common Mineral Associations

Calcite, Rhodonite, Quartz, Spessartine, Willemite

Distingushing Similar Minerals

Willemite - Different cleavage, fluoresces bright green.
Rhodonite - Usually pinker in color.

tephroite Photos



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