<Original Papers>Cryptomelane Nodules from the Tachikawa Mine, Iwate Prefecture

The bedded manganese ore deposits at Tachikawa Mine, Iwate Prefecture, occur in the chert of palaeozoic age. In the upper zone of the deposits, the ore consists of yokosukaite, pyrolusite, todorokite and cryptomelane, but in the lower zone, it consists mainly of the manganese dioxide minerals mentioned above and braunite with a small quantity of rhodonite, spessartite, penwithite, rhodochrosite and quartz. Cryptomelane commonly occurs in veinlets along fractures or as spherical nodules filling cavities in the oxidized zone of the deposits. The investigated spherical specimen of cryptomelane measures 20 centimeters in diameter and can be divided into roughly three main parts, namely, inner, middle and outer zone, and each parts shows colloform banding on a fine scale. Chemical, physical, thermal and X-ray data for three parts of this specimen are given