Todorokite - Appearance

Appearance

Todorokite occurs as spongy banded and reniform (kidney-shaped) aggregates composed of minute lathlike crystals. The crystals are flattened parallel to the plane containing the a and c crystal axes, and elongated parallel to the c axis. Minerals of the hollandite-cryptomelane and romanèchite groups also have fibrous or acicular habits and two perfect cleavages parallel to the fiber axis. Todorokite is dark brown to brownish black in color and brown in transmitted light. It has a black to dark brown streak and the luster is metallic to dull, but silky in aggregates. It is opaque in all but the thinnest slivers, which are transparent.

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