What is Johannsenite?
Johannsenite is a manganese-rich calcium pyroxene, usually found in skarns and metamorphic rocks as brown, green or grey crystals.
Mineralogy and crystal structure
Reference formula: CaMnSi2O6. Johannsenite has the monoclinic clinopyroxene structure and forms compositional series with hedenbergite and diopside. It is the low-temperature polymorph of CaMnSi2O6, while bustamite is the high-temperature polymorph. Johannsenite is classified with silicates and has a monoclinic crystal system. Typical hardness is 5–6 on the Mohs scale and specific gravity is approximately 3.5–3.6.
Colour, lustre and habit
Typical colours include brown, green, blue-green, grey. The usual prismatic, granular, massive habit and vitreous lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Johannsenite forms in or is associated with manganese-bearing skarns, contact-metamorphic limestones and metamorphosed ore deposits. Important documented localities include Italy, the United States, Mexico, Bulgaria, South Africa and Japan.
A collector's window into skarn chemistry
Johannsenite is a strong choice for a petrology-focused collection because its colour and crystal habit reflect manganese-rich fluid interaction with carbonate rocks. It pairs especially well with other pyroxenes and garnet-group minerals from the same skarn.
The mineral named for a petrologist
Johannsenite's name honours the geologist Albert Johannsen, giving the species a natural connection to the history of petrology. Modern symbolic readings are optional; the documented naming and phase relationship are the more compelling story.
Collecting and care
Protect cleavage edges and keep the skarn or ore association with the specimen; do not identify it from colour alone.
