This is an intricate cabochon made of Psilomelane banded with Pyrolusite - it forms alternating dark and lighter bands. It is exceptionally hard to photograph. The base color is black, and the patterns are in near-black. If you look closely, you can see them - they almost resemble Damascus steel in pattern. This cab is exceptionally well-finished, and just gleems in person.
Psilomelane is named after the Green term "psilos", meaning smooth, and "melas", meaning black. Psilomelane consists of hydrous manganese oxide with variable amounts of barium and potassium.