tephroite


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tephroite

[′tef·rō‚īt]
(mineralogy)
Mn2SiO4 An olivine mineral that occurs with zinc and manganese minerals.
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2MnO + Si[O.sub.2] [approaches] 2MnO*Si[O.sub.2] tephroite
When comparing the Gibbs Free Energy of Formation for mullite, fayalite and tephroite, the reactions between the iron- and manganese oxides and the silica will have the following values:
[Delta][G.sub.form] 2MnO*Si[O.sub.2] (tephroite) = -3370 cal/mole
Iron- and manganese oxides will react with the silica component of the mullite to form fayalite and tephroite, respectively.
Unfortunately, the silicate portion is affected by iron- and manganese oxides in a way similar to that which a silica-based refractory is affected, forming low temperature fayalite or tephroite. As this sintering agent is dissolved, the matrix will erode.
The Val Graveglia manganese mines have produced some rare and uncommon species (bementite, ganophyllite, sarkinite, sussexite, tephroite etc.) reported from just a few other famous localities, such as Langban, Sweden, and Franklin and Sterling Hill, New Jersey (Holstam and Langhof, 1999; Frondel and Baum, 1974).
It occurred very sparingly at the surface of cavities and fractures in a manganese ore containing tephroite, bementite, braunite, hausmannite and hematite.
The Gambatesa mine produced some specimens of pale amethyst quartz associated with tephroite and hausmannite.
Sussexite fills thin fractures and is associated with calcite, tephroite, rhodochrosite, sarkinite and reppiaite (Cortesogno et al., 1979).