ПСЕВДОТЕТРАЭДРИЧЕСКИЕ КРИСТАЛЛЫ ГРАНАТА - ИСТОРИЯ РОСТА

Abstract

Unusual pseudotetrahedral (43m) skeleton-zonal crystals of garnet, with false simple forms {211}. {211}, (321), (321} and (110), have been found in metasomatites at the Viluy River (Russia, Yakutia). These crystals represent hibschite (GrsvAndi) monocrystal spongy pseudomorphs of achtarandite after an unknown 43m tetrahedral mineral, covered with die later epitaxial films of Fe-gross и la re. Two morphologic series_of pseudotetrahedral crystals were recorded, depending on achtarandite crystals forms {211} and/or {211} + {211}. Tendency of the development of rombododecahedron {110} or tetragontrioctahedron (211} faces on the epitaxial Him of grossular, in its turn, predetermines development of regenerated forms of pseudotetrahedral crystals. If {110} faces dominate in the grossular facing, there should be expected to appear the skeleton-like tetrahedral crystals delimitated by re-entrant faces into four volumes, each of mem with symmetry close to m3m. If {211} faces dominate, the crystal would take gradually die isometric tetragontrioctahedral form with the m3m symmetry.