| Research Abstract |
Manganese dioxide minerals are major components of manganese deposits on land and ferromanganese nodules on sea-floor. Accurate identification of these minerals is generally not easy because they are often fine-grained, poorly crystalline, and intimately intergrown. It is still not clarified how much information on the identities can be obtained by using a reflected-light microscope which is the basic instrument for the examination of ore minerals, hence we consider that it is important to make clear the limit of usefulness of the microscopy in order to correctly and rapidly gain available information regarding the mineral texture and paragenesis. For that purpose we first review the basic mineralogy and crystal chemistry of 21 naturally-occurring manganese dioxides and secondly according to the numerical resemblances of reflectance(R)and Vickers microhardness(VHN)which are the most important quantitative parameter that can be used to identify ore minerals we classify the minerals into
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four groups from I to IV in decreasing order of both the values. Thirdly we make R and VHN measurements on representative manganese dioxides from manganese deposits in Japan and India to evaluate those values cited from references. The result obtained is concordant with it from references and the 21 minerals are divided as follows : I group(pyrolusite and nsutite), II group(cryptonelane, hollandite, coronadite, manjiroite, romanechite, woodruffite, and ramsdellite), III group(chalcophanite, aurorite, birnessite, lithiophorite, todorokite, asbolane, and janngunite), and IV group(vernadite, rancieite, takanelite, akhtenskite, and buserite). It is characteristic of this classification that the minerals in I, II, and III and IV groups substantially have chain, tunnel, and layer structures respectively and have increasing water content in ascending order of the number of group. We conclude that it is possible to identify most of these minerals under the reflected-light microscope by itself when the individual minerals are carefully examined with respect to the distinctive features for optical properties and mineral texture and paragenesis along with R and VHN. Less
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