Calcite and ? on dolomite from Germany – miniature

Calcite and ? on dolomite from Germany – miniature
€10.00

Calcite and ? on dolomite from Grevenbroich, Rhein-Kreis Neuss, Germany
I couldn’t identify the brownish/black shiny minerals on it. There is also some limonite on the piece
7 cm x 4.3 cm
77 gram