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www.mineralgallery.co.za Minerals P-T |
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Tephroite |
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Name
Tephroite
Chemistry
(Mn,Mg,Zn)2SiO4
Uses
As a mineral specimen
Color
Ash gray, grayish red, red, bluish red and yellowish green
Hardness
6
Specific gravity
4.1
Streak
White to gray
Crystals
Prismatic to blocky crystals Also massive, granular and compact
Accompanied by:
Richterite, Rhodonite, Schefferite
Similar to:
Willemite
Named after the Greek word "tephros" meaning ash gray. An international rare mineral with a few good localities in Sweden.
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Langban, Varmland. Grainy to dense aggregates with grayish red color.
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Harstigen, Varmland. Commonly as bluish gray masses.
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Jakobsberg and Brattforsgruvan, Nordmark, Varmland
and we represent the
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Kalahari Manganese field. Wessels mine. As distinct red crystals.
Crystals of tephroite are rare, and the mineral is commonly found in coarse granular form, breaking into rectangular blocks with rudely striated faces. The cleavage is distinct parallel to the base and to the brachypinacoid and is therefore rectangular. The hardness is 5.5 to 6, and the specific gravity is 3.87 to 4.1. The crystals are bluish-green by daylight and pink by artificial light, resembling in this respect the closely related mineral glaucochroite. The color of the granular material is ash-gray, brown, red-brown, and flesh-red and is darker or black oil weathered surfaces. Some of the color is due to included zincite. The luster is vitreous to greasy. Tephroite is easily mistaken in some of its forms for willemite, as it has the same luster and color range as the variety troostite. Its better and distinctly rectangular cleavages are a definite means for its identification
Tephroite is essentially an orthosilicate of manganese, commonly containing more or less magnesium, zinc, iron, or calcium, or several of those metals.
In all the analyses there is sensible conformity to the accepted ratios for the orthosilicate formula—different amounts of magnesium and zinc and, to a less extent, iron and calcium taking the place of part of the manganese. Brush was of the opinion that the zinc found in all analyses is present in included zincite, but that this is not invariably true is shown by the fact that the molecular ratios in some analyses more nearly satisfy the orthosilicate formula when zinc is regarded as essentially a part of the mineral rather than as a constituent of mechanical inclusions.
Tephroite is one of the unusual minerals found at the famous mines of Sterling Hill and Franklin, New Jersey, USA. It is named for the typical color which is ash gray ("tephros" is Greek for ash colored). Tephroite forms a series with the olivine mineral fayalite. Tephroite is the manganese rich member of the series and fayalite is the iron rich member with a formula of Fe2SiO4. Unlike fayalite which is more commonly found in volcanic rocks, tephroite is a contact metamorphic and hydrothermal replacement mineral.
This rare manganese olivine has been found as light-red to dark red crystals up to 2 cm at the Wessels mine. They are closely associated with jacobsite, gageite and calcite.
See the following website for a comprehensive list of localities where tephroite has been found. http:/www.mindat.org/min-3913.html
