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 {1 1 2} and a minor rhombic dodecahedron form {1 1 0}. This is in contrast with all other natural garnet crystals for which {1 1 0} is always more important than {1 1 2}. Theoretical growth forms derived from attachment energy calculations indicate that {1 1 0} should be the dominant form for all natural garnets. Spessartine crystals were grown experimentally at atmospheric pressure and at temperatures of 1175-1195 degreesC from a molten stoichiometric mixture of tephroite (Mn2SiO4), gamma -alumina (Al2O3) and quartz (SiO2). Their habit is identical to that of natural grown spessartine crystals. The specific {1 1 2} spessartine habit may be caused by the presence of Mn3+ during the growth as an impurity. (C) 2001 Elsevier Science B.V. All rights reserved.