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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.
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Chemical Formula |
CaMnSi2O6 |
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Composition |
Calcium manganese silicate, sometimes with iron |
| Variable Formula |
Ca(Mn,Fe)Si2O6 |
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Color |
Gray, brownish-gray, greenish-gray, olive-green, light blue, cream yellow. May also be banded. |
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Streak |
White |
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Hardness |
5 - 6 |
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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. |
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Transparency |
Translucent to nearly opaque |
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Specific Gravity |
3.4 - 3.6 |
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Luster |
Vitreous to greasy |
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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. |
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Fracture |
Uneven to splintery |
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Tenacity |
Brittle |
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In Group |
Silicates; Inosilicates; Pyroxene Group |
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Striking Features |
Crystal habits, localities, color, and cleavage habits |
| Environment |
Manganese-rich deposits of contact metamorphic rocks.
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Popularity (1-4)
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3 |
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Prevalence (1-3)
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3 |
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Demand (1-3) |
3 |
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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.
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The localities and crystal habits of this mineral can distinguish from most minerals.
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