Acta Musei Moraviae

Ferrobustamite-bearing magnetite skarn in marble at Sokolí near Třebíč (Moldanubian zone, Western Moravia)

Ferrobustamite was found in Fe-skarn at Sokolí and it is the first known occurrence in the Bohemian Massif. The skarn forms layer in marble enclosed in leucocratic migmatites (diatexites). Ferrobustamite (Ca_4.58–4.70 Mn_0.14–0.20 Mg_0.01–0.13)₅ Fe_0.95–1.6 Si_5.86–6.01 O₁₈) forms microscopic needle-like aggregates with hedenbergite (Hd_71–99) filling intergranulars of grossular-andradite. It forms a massive skarn (endoskarn) whereas exoskarn is composed of andradite + hedenbergite + abundant magnetite with microscopic inclusions of gahnite. The adjacent calcite marble is very poor in flogopite, diopside, and rare hydroxylchondrodite. Marble locally contains veins of diopside, prehnitized anorthite and wollastonite. The mineral assemblage of ferrobustamite is a product of HT/LP-MP metamorphism (skarnization) at T > 600 ° C in the contact aureole of the Třebíč pluton (Moldanubian Zone).