REGENERATION GROWTH OF SOME HEXAGONAL (TRIGONAL) CRYSTALS UNDER HYDROTHERMAL CONDITIONS. L.N. Demianets Institute of Crystallography, RAS, Moscow, Russia

The specific features of the regeneration growth (RG) of nepheline Na₃KA₁₃Si₃O₁₂, beril Be₃A₁₂Si₃O₁₂, ruby A1₂O₃:Cr, GaPO₄ were studied. The preferable directions of RG were found on the base of kinetic and crystallographic data. The equilibrium and non-equilibrimn growth forms were established for the crystals mentioned above. The morphologies of the singular and regeneration planes were investigated.

For these crystals very low normal growth rates are typical and we need to search for the new ways to grow large high-quality single crystals. One of the way is to use the RG when regeneration planes are used as seeds. The regeneration planes are known to be absent in the crystal endhabit built up by the flat F-faces.

For nepheline the planes {10.1} and {11.0} are found to be the regeneration planes while the monohedra (00.1), (00.1) and prism {10.0} are the faces of equilibrium growth form which are present in the final habit of crystals. Multi-head growth surface is characteristic for the faces of pyramid {10.1} and prism {11.0} .

In the case of beril the equilibrium form consists of the pinacoid (00.1} , pyramids {11.2} , {10.2} and prism {11.0} . The RG directions are perpendicular to {11.1} or {11.4} planes. Multy-head growth is typical for these planes. The regeneration planes are perpendicular to {10.0} .

For ruby, the faces {11.3} , {00.1} and {10.0} represent the equilibrium habit of crystal. RG occurs in the directions perpendicular to {10.5} , {10.3} , {10.10} directions. Thin striations parallel to {00.1} is typical of {10.0} faces.

All the crystals demonstrate the best quality if the regeneration plane is perpendicular to one of the equilibrium form which is growing due to spiral-layer mechanism.