Tephroite

Tephroite is a manganese bearing olivine group mineral probably best known from its type locality, the Sterling Mine of New Jersey, USA.

Avoid confusing this mineral ‘tephroite’ with the volcanic rock ‘tephrite’.

Information about Tephroite

Tephroite is a member of the olivine group and typically forms as massive, granular aggregates rather than well-developed crystals. It is commonly found in manganese-rich metamorphic deposits.

The mineral ranges in colour from bluish grey, greenish grey, and brownish grey to a characteristic ash-grey tone (from which its name derives, from the Greek tephros, “ash-coloured”). It is usually opaque, but thin fragments may be translucent. Its lustre is vitreous to greasy, and broken surfaces can appear dull.

 

Uses and History

Tephroite itself is not an industrial ore, though it can be a minor manganese source. Its primary importance is scientific, as it provides insights into metamorphic processes in manganese-rich environments. Collectors value tephroite for its rarity and association with other striking manganese minerals, such as rhodonite and spessartine.

 

Tephroite was first described in 1823 by Johann Friedrich August Breithaupt. Its type locality is claimed as the Sterling Mine, USA – I am not sure whether Breithaupt received material from Sterling Mine or visited.

Its name comes from the Greek tephros, meaning “ash-coloured,” referencing its distinctive grey hues. It has since been reported in various manganese-rich localities worldwide, including the USA, South Africa, and Japan.

 

Mineralogy

Chemistry
A manganese nesosilicate mineral with the formula Mn2SiO4.
Colours and Variations

Green, blue green, grey, red, red-brown.

Streak
Pale grey
Luster
Vitreous to greasy
Transparency
Transparent to translucent
Fracture
Uneven to conchoidal
Crystal habit
Crystals are typically short and prismatic. Often in grains, compact, or massive.
Mohs hardness
6
Tenacity
Brittle.
Fluorescence
Specific Gravity
3.87 – 4.15
Easiest testing method
Common occurences
Typically found in Fe-Mn ore deposits.

Hazards and Warnings

Mineral collectors should wash their hands after handling specimens, to avoid any exposure to potential toxins.
Almost all rocks, minerals (and, frankly, almost all other substances on earth) can produce toxic dust when cutting, which can cause serious respiratory conditions including silicosis. When cutting or polishing rocks, minerals, shells, etc, all work should be done wet to minimise the dust, and a suitable respirator or extraction system should be used.

 

Translations

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English:

Italian:

Russian:

  • Тефроит

French:

Japanese:

Spanish:

  • Tephroit

German:

  • Tephroit

Korean:

Thai:

Gujurati:

Mandarin Chinese:

  • 锰橄榄石

Urdu:

Further Reading / External Links