Stannian andradite occurs with pyroxene and carbonates, with blende and pyrite as accessories in a skarn deposit in the Plavno mine, Krušné Hory Mts., NW. Bohemia. The green crystals are rhombic dodecahedra up to 3 cm in size. Sp. gr. 3·78; n 1·879; a 12·079±0·002 Å. Quantitative chemical and spectrographic analyses are given; the composition is (Ca_2·96Mg_0·04Mn_0·02)_3·02 (Fe1·793+Al0·18)1·97 (Si_2·95Sn_0·04)_2·99O₁₂. The content of tin (SnO₂ 1·07 %) is isomorphously bound in the lattice, and according to crystallochemical calculations the entrance of tin into the garnet lattice is most probably due to substitution of SnO44− for SiO44−. The presence of tin in the andradite shows that this element was already present in the metasomatic solutions during the process of skarnization.