Acta Musei Moraviae

Gayite from granitic pegmatite at Cyrilov near Velké Meziříčí, Moldanubicum

Gayite, a new dufrenite group mineral with Mn as dominant divalent cation was recently described by KAMPF et al. (2010) from beryl-columbite-phosphate type granitic pegmatite in Cordoba province, Argentina. Similar, Mn-dominant member of the dufrenite group occurs in association with natrodufrenite, mitridatite, fluorapatite and crandalite group minerals at the border of the Al-phosphate nodule from Cyrilov pegmatite, whereas its chemical composition differs from the type locality gayite. The elevated content of Ca (0.18–0.33 apfu; 1.20–2.13 wt. % CaO), Mg (≤ 0.15 apfu Mg (≤ 0.68 wt. % MgO), variable Al (0.01–1.03 apfu; 0.05–6.14 wt.% Al₂O₃) and ratio Mn/(Mn+Fe²⁺) 0.30–0.81 is typical for natrodufrenite to gayite form Cyrilov. Substitution trends are briefly discussed.