Tephroite and Willemite (FOV 2.3 x 3.0 mm) Locality: Franklin Mine, Franklin, Franklin Mining District, Sussex County, New Jersey, USA Tephroite gets its name f — Photo: Modris Baum · Public domain
Tephroite
The manganese end-member of the olivine group — gray-green masses in manganese skarns.
Intro adapted from Wikipedia (CC BY-SA).
Tephroite is an IMA-recognized mineral species in the silicate class, with the chemical formula Mn²⁺₂(SiO₄).
It crystallizes in the orthorhombic crystal system (space group Pbnm). It is a member of the Olivine structural group.
Key properties: Mohs hardness 6; specific gravity 3.87–4.12; typically brown or red or gray; Pale gray streak; Vitreous to greasy luster; refractive index 1.805; optically biaxial.
IMA symbol Tep, grandfathered status — known before the IMA’s founding, named in 1823.
Found in Fe{Mn ore deposits, related skarns, and metamorphosed manganese-rich sediments.
It is found associated with Zincite, willemite, franklinite, rhodonite, jacobsite, diopside, gageite, bustamite, manganocalcite, glaucochroite, calcite, banalsite, alleghanyite.
Its name comes from the Greek for ash-colored.
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