1911 Encyclopædia Britannica/Manganite

by Leonard James Spencer

MANGANITE, a mineral consisting of hydrated manganese sesquioxide, Mn₂O₃·H₂O, crystallizing in the orthorhombic system and isomorphous with diaspore and göthite. Crystals are prismatic and deeply striated parallel to their length; they are often grouped together in bundles. The colour is dark steel-grey to iron-black, and the lustre brilliant and submetallic: the streak is dark reddish-brown. The hardness is 4, and the specific gravity 4.3. There is a perfect cleavage parallel to the brachypinacoid, and less perfect cleavage parallel to the prism faces m. Twinned crystals are not infrequent. The mineral contains 89.7% of 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 barytes in veins traversing porphyry. Crystals have also been found at Ilmenau in Thuringia, Neukirch near Schlettstadt in Alsace (“newkirkite”), Granam near Towie in Aberdeenshire, Upton Pyne near Exeter and Negaunee in Michigan. As an ore of manganese it is much less abundant than pyrolusite or psilomelane. The name manganite was given by W. Haidinger in 1827: French authors adopt F. S. Beudant’s name “acerdèse,” (Gr. ἀκερδής, unprofitable) because the mineral is of little value for bleaching purposes as compared with pyrolusite.  (L. J. S.)