CHAPTER X 
ORES OF MANGANESE AND CHROMIUM 
MANGANESE 
Tue ores of manganese (Mn; at. wt, 55; sp. gr., 77; 
melting-point, 2275° F.) are constantly associated with those 
of iron. Its main service is as an alloy with iron, which it 
hardens and strengthens; it is used as a flux, a pigment, 
in drugs, and in chemicals. Manganese is widely distributed 
in rock-forming minerals, as in the pyroxene rhodonite 
(Mn8iO3; Mn 41-8 per cent), hortonolite, a variety of 
olivine, and spessartite, manganese-garnet. Like iron it 
readily oxidizes, and is deposited in sedimentary beds, as 
replacements, and as earthy mixtures of hydrous oxides, 
such as wad and psilomelane. The black oxide, pyrolusite, 
(MnO,; Mn 63 per cent.) occurs as a black stain and in 
dendrites, the plant-like growths on joint planes. The 
manganese carbonate, rhodochrosite (MnCO,;; Mn 47-8 
per cent) is a common veinstone. Manganese is sparse 
in most igneous rocks, but abundant in those of certain 
areas; thus the Kodurite Series of India ranges from acid 
to ultra-basic, but all its rocks have above the average 
proportion of manganese (L. L. Fermor, G.S. India, Mem. 
xxxvii, p. 250). The ready concentration of manganese 
helps its deposition in lodes along faults or fissures, as in 
Central Germany and Japan, and in nodular replacement 
masses, as in the Kodurite Series of Vizagapatam in India. 
Manganese ores, like those of iron, occur under very varied 
conditions ; but those of most economic value are secondary 
concentrations derived originally from igneous rocks. The 
bedded ores have been mined from many geological horizons, 
e.g. the Ordovician of North Wales, the Devonian of North 
Devon, and near Coblenz and Giessen, in Germany, the 
Oligocene at Nicopol in Southern Russia, and the Lower 
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