Manganite

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Manganite is a mineral. Its composition is manganese oxide-hydroxide, MnO(OH), crystallizing in the orthorhombic system and isomorphous with diaspore and goethite. Crystals are prismatic and deeply striated parallel to their length; they are often grouped together in bundles. The color is dark steel-grey to iron-black, and the luster brilliant and submetallic. The streak is dark reddish-brown. The hardness is 4, and the specific gravity is 4.3. There is a perfect cleavage parallel to the brachypinacoid, and less-perfect cleavage parallel to the prism faces. Twinned crystals are not infrequent.

The mineral contains 89.7% manganese sesquioxide; it dissolves in hydrochloric acid with evolution of chlorine. The best crystallized specimens are those from Ilfeld in the Harz, where the mineral occurs with calcite and barite in veins traversing porphyry. Crystals have also been found at Ilmenau in Thuringia, Neukirch near Sélestat in Alsace (newkirkite), Granam near Towie in Aberdeenshire, and in Upton Pyne near Exeter, UK and Negaunee in Michigan, United States. As an ore of manganese it is much less abundant than pyrolusite or psilomelane.

Color is black to steel gray. Luster is metallic to dull in weather specimens. Transparency: Crystals are opaque, translucent in only thin splinters. Crystal System is monoclinic; 2/m Crystal Habit is typically short prismatic crystals that have a pseudo-orthorhombic shape. The terminations are generally blunted with domes and minor pyramid faces. The crystals are striated lengthwise. Crystals are usually grouped into tight bundles and columnar, massive and fiberous forms are also known. Penetration and contact twinning does occasionally occur. Cleavage is perfect in one direction lengthwise and good to fair in two other directions, one lengthwise at near right angles to the first one and one basal. Fracture is uneven. Hardness is 4 Specific Gravity is 4.3 (average for metallic minerals) Streak is reddish to brownish black. Associated Minerals are calcite, barite, garnets, limonite, siderite, pyrolusite and other manganese minerals. Other Characteristics: Alters to pyrolusite which can coat the crystals, dulling the luster and can affect a streak test. Notable Occurrences include Cornwall, England; Harz Mts., Germany; China; Sterling Hill, New Jersey and Negaunee, Michigan, USA and Ukraine. Best Field Indicators are crystal habit, luster, striations, color and streak

The name manganite was given by W. Flaidinger in 1827.

References

• This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.