Gahnite from Siedlimowice, Strzegom-Sobótka granitic massif, SW Poland

Green spinel was found in a vein pegmatite in Siedlimowice (Strzegom-Sobótka massif,SW Poland). X-ray diffraction and electron microprobe analyses allowed defining the mineral as gahnitewith the formula (Zn6.1Fe1.8Mn0.1)(Al15.8Fe0.2)O32 and unit cell parameters a = 8.1018 ± 0.008 ,V = 531.787 ± 0.156 3. Its chemical composition is typical of gahnites of igneous association. Formationof the zincian spinel was most probably controlled by local variations of crystallization conditions, e.g. thevariations of a Zn/Fe ratio in a pegmatitic fluid or of oxygen fugacity.