Acta Musei Moraviae

Green chromium-bearing mica in Balinka Conglomerates of Rosice-Oslavany Formation (Upper Carboniferous) at Oslavany

Clasts of light-green mica containing chromium were recorded in the Upper Carboniferous conglomerates at Oslavany (Rosice-Oslavany Coalfield, Boskovice Graben). It is a potassium-deficient muscovite to illite (0.514–0.912 apfu K) with 0.88–2.29 wt. % Cr₂O₃ (0.046–0.119 apfu Cr). Slightly increased both Mg (0.180–0.440 apfu Mg) and Fe (0.151–0.169 apfu Fe) contents also were detected. Mica is very low in Ti (< 0.003 apfu), V (< 0.002 apfu), Mn (< 0.002 apfu) and F (<0.052 apfu); Ba lies below detection. The origin of the clastic material of the Balinka conglomerates can be found in the crystalline complexes in the vicinity. Chromium-bearing mica could originate from hydrothermally altered spinel peridotites or other ultramafics of adjacent Moldanubicum (Gföhl Unit) or Moravian unit.