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The Mineral manganoneptunite
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Manganoneptunite is the manganese-dominant variant of Neptunite, having a greater portion of manganese over iron in a solid solution series. Although often considered a variety of Neptunite, the IMA recognizes Manganoneptunite as a distinct mineral species. Manganoneptunite is generally ligher in color than Neptunite, and can even be completely transparent in specimens where the iron content is very low. |
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Chemical Formula |
KNa2Li(Fe2+,Mn)2Ti2Si8O24 |
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Composition |
Silicate of potassium, sodium, lithium, manganese, iron and titanium |
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Color |
Red, dark red, orange, brown, dark brown, black |
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Streak |
Dark brown |
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Hardness |
5 - 6 |
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Crystal System |
Monoclinic |
Crystal Forms
and Aggregates |
As small tabular and prismatic crystals with a square cross-section. Also in complex crystals with many faces, and in tabular crystals with rhombic faces.
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Transparency |
Transparent to nearly opaque |
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Specific Gravity |
3.2 - 3.3 |
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Luster |
Vitreous |
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Cleavage |
1,1 - with 80 and 100 degree angles |
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Fracture |
Conchoidal |
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Tenacity |
Brittle |
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In Group |
Silicates; Nesosilicates |
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Striking Features |
Color and crystal habits, perfect cleavage, and locality/mode of occurrence. |
| Environment |
In nepheline syenite pegmatites. |
| Rock Type |
Igneous |
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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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Manganoneptunite is not a common mineral, and is only found is a limited amount of deposits worldwide. The most notable locality for this mineral is Mont Saint-Hilaire, Québec, Canada, where small transparent, orange to dark-red crystals occur. Darker colored crystals are found nearby at the Demix-Varennes quarry, Varennes & St-Amable, Québec. Black lustrous Manganoneptunite crystals have been fround in the Aris Quarry, Windhoek District, Namibia; and black-cherry-red crystals from the Kola Peninsula in Russia.
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Neptunite - Usually darker in color. Manganoneptunite also rarely forms in large crystals, as does Neptunite.
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