There are quite a few manganese ore deposits in the Bistrița Mountains, the most significant of which is Iacobeni. These are characterized by the predominance of manganese silicates, the largest amount of which is rhodonite (MnSiO3) and, to a lesser extent, manganogrunerite, spessartine and tephroite. Rhodochrosite (manganese carbonate, MnCO3) is also common, and of course, manganese oxides are also present (nsutite, cryptomelane, manganite, birnessite). Quite a few world-rare manganese minerals have been detected in Iacobeni (e.g., sonolite, alleghanyite, bannisterite, nambulite, friedelite, mcgillite, caryopilite, etc.). Because the two most common minerals (rhodonite and rhodochrosite) are pink, this colour dominates these ore samples. Their large crystals do not occur here, they appear mostly in massive aggregates, which is why we present them mainly as polished sections in our exhibition.
In the picture: Rhodonite-containing polished section, Iacobeni (Romania). Size: 17 cm. Photo by Géza Kulcsár.