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Olive-Green Johansennite

The Mineral johannsenite




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.
Chemical Formula CaMnSi2O6
Composition Calcium manganese silicate, sometimes with iron
Variable Formula Ca(Mn,Fe)Si2O6
Color Gray, brownish-gray, greenish-gray, olive-green, light blue, cream yellow. May also be banded.
Streak White
Hardness 5 - 6
Crystal System Monoclinic
Crystal Forms
and Aggregates		 As elongated and stubby prismatic crystals, in thick tabular crystals, in radiating and fibrous aggregates, massive, and in rounded masses.
Transparency Translucent to nearly opaque
Specific Gravity 3.4 - 3.6
Luster Vitreous to greasy
Cleavage 1,2 - prismatic at cleavage angles of 87º and 93º (Characteristic of minerals in the pyroxene group). May also exhibit parting in one direction.
Fracture Uneven to splintery
Tenacity Brittle
In Group Silicates; Inosilicates; Pyroxene Group
Striking Features Crystal habits, localities, color, and cleavage habits
Environment Manganese-rich deposits of contact metamorphic rocks.
Rock Type Metamorphic
Popularity (1-4) 3
Prevalence (1-3) 3
Demand (1-3) 3


Johannsenite AUCTIONS




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.

COMMON MINERAL ASSOCIATIONS
Rhodonite, Bustamite, Pyrolusite, Sphalerite, Quartz, Calcite, Wollastonite

DISTINGUISHING SIMILAR MINERALS
The localities and crystal habits of this mineral can distinguish from most minerals.


johannsenite PHOTOS
 
ADDITIONAL RESOURCES
 
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