What is Piemontite?
Piemontite is a manganese-bearing epidote-group mineral with red to violet colour, especially attractive in metamorphic rocks and lapidary material.
Mineralogy and crystal structure
Reference formula: Ca2Al2Mn3+Si3O12(OH). Piemontite is monoclinic and forms a compositional series with epidote-group minerals. Manganese content drives its warm red-purple colour and optical character. Piemontite is classified with silicates and has a monoclinic crystal system. Typical hardness is 6–7 on the Mohs scale and specific gravity is approximately 3.4–3.6.
Colour, lustre and habit
Typical colours include red, purple-red, brown, pink. The usual prismatic, granular, massive habit and vitreous, pearly lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Piemontite forms in or is associated with manganese-rich metamorphic rocks, veins and altered volcanic or sedimentary manganese deposits. Important documented localities include Italy, Japan, Austria, South Africa, Mexico and the United States.
Red-violet epidote-group colour
Piemontite adds a rich red note to metamorphic mineralogy. Its manganese-bearing structure turns an epidote framework into a visually distinctive collector material.
Collecting and care
Protect polished material from scratches and acids; preserve matrix because the host rock is often diagnostic.
