Melt growth of spessartine (Mn₃Al₂Si₃O₁₂)

The habit of spessartine (Mn₃Al₂Si₃O₁₂) garnet crystals grown in nature is determined by the presence of a large icositetrahedral crystal form {112} and a minor rhombic dodecahedron form {110}. This is in contrast with all other natural garnet crystals for which {110} is always more important than {112}. Theoretical growth forms derived from attachment energy calculations indicate that {110} should be the dominant form for all natural garnets. Spessartine crystals were grown experimentally at atmospheric pressure and at temperatures of 1175-1195°C from a molten stoichiometric mixture of tephroite (Mn₂SiO₄), γ -alumina (Al₂O₃) and quartz (SiO₂). Their habit is identical to that of natural grown spessartine crystals. The specific {112} spessartine habit may be caused by the presence of Mn³⁺ during the growth as an impurity.