Manganoneptunite is the manganese-dominant variant of Neptunite, having a greater portion of manganese over iron in a solid solutionseries. 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.
Crystal Forms & 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.
Striking Features
Color and crystal habits, perfect cleavage, and locality/mode of occurrence.
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.
