クリプトメレーン鉱―万次郎鉱―ホランド鉱系鉱物

抄録

The chemical analyses were made on twenty four cryptomelanes, five manjiroites and two hollandites from northeastern Japan after the confirmation of their purity though X-ray and thermal studies. These results and analytical data on many for eign samples lead to the general formula A_1±xMn₈O₁₆·nH₂O, where A represents large ions such as K⁺, Na⁺, Ba²⁺, Ca²⁺, Pb²⁺etc., Mn is chiefly Mn⁴⁺ with a small quantity of medium and small-sized ions such as Mn²⁺, Mg²⁺, Fe³⁺, Al³⁺ etc. n is between 0 to 2 and the average 1.2. The value of 1+x ranges between 1.28 and 0.17 and the average is 0.88. X-ray diffraction patterns of Japanese cryptomelane-manjiroite series can be indexed in terms of a body-centered tetragonal unit cell. Lattice constant a₀ of this series varies appreciably but somewhat systimatically with the variation in the Na/Na+K ratio, whereas c₀ varies little.
Heating experiments of cryptomelane, manjiroite and hollandite in air established the following process of thermal transformation:
cryptomelane manjiroite hollandite → approx. 600°C α-Mn₂O₃ (bixbyite) → approx. 900°C tetr. Mn₃O₄ + X phase. (hausmannite)
In th case of cryptomelane X phase had been considered to be the remnant of the small amount of untransformed cryptomelane, but the present study shows that the X phases of three heated minerals were the compounds belong to the systems K₂O-, Na₂O- and BaO-manganese oxide respectively.