SILICATES; INOSILICATES; PYROXENE GROUP · MONOCLINIC

Johannsenite

CaMnSi₂O₆

Hardness: 5–6
Streak: White
Spec. Gravity: 3.4–3.6
System: Monoclinic

About

Johannsenite is a rare member of the pyroxene group that is isomorphous with Diopside and Hedenbergite. It often occurs with black manganese oxide dendrites on its surface. Johannsenite alters to become the pink mineral Rhodonite. Johannsenite is named in honor of Albert Johannsen (1871-1962), a petrologist and professor at the University of Chicago.

Crystal Forms & Aggregates

As elongated and stubby prismatic crystals, in thick tabular crystals, in radiating and fibrous aggregates, massive, and in rounded masses.

Striking Features

Crystal habits, localities, color, and cleavage habits

Environment

Manganese-rich deposits of contact metamorphic rocks.

Noteworthy Localities

Johannsenite is found in slender acicular crystals and in banded masses at Monte Civillina, Recoaro, Italy; and in olive green crystals in the North Mine, Broken Hill, New South Wales, Australia. Brown crystals associated with Rhodochrosite come from the Uchucchaqua Mine, Oyon Province, Peru. In the U.S., the premier locality is the Iron Cap mine, Landsman Camp, Graham Co., Arizona. Other occurrences are Hanover, Grant County, New Mexico; and Franklin, Sussex Co., New Jersey.