Crystal growth of tourmaline connected to a number of difficulties such as high temperature and pressure of crystallization, low growth rate, etc. [1,2]. At the same time, the synthesis of structural analogues of natural minerals in which aluminum and silicon are completely or partially substituted by gallium and germanium (gadolinium gallium, yttrium aluminum, and yttrium iron garnets, germanium oxide, etc.) can reduce significantly the temperature and pressure of the process and to improve functional properties.
Studies were performed under thermogradient conditions using chromium–nickel alloy autoclaves at temperature of 450-650°C and pressure of 100 MPa. Plates made from natural tourmaline crystals of elbaite (chemical formula is Na(Li,Al)₃Al₆Si₆O₁₈(BO₃)₃(OH,F)₄) were used as seed crystals in the experiments. Single crystals of quartz and corundum with addition of gallium oxide was used as charge material. The autoclave was filled with solution of boric acid and mineralizer in accordance to autoclave-filling factor,then sealed, and placed into electric furnace with two-section heaters. The duration of the runs was 14 days.
As a results, the epilayer of Ga-rich tourmaline wherein part of aluminum are substituted by gallium was grown on natural elbaite seed for the first time. The thickness of this layer was up to 100 µm, and the gallium content was up to 12 wt. %. Along with epilayer of Ga-rich tourmaline, a small amount of fine (10-30 micron in size) long prismatic Ga-rich tourmaline crystals of spontaneous nucleation was observed on surface of the seed and in the charge.
This work was supported by the RFBR (Grant no. 12-05-31030) and Ministry of education and science of Russian Federation (Agreement no. 8612 and 8378).
[1] London, D. (2011) Canadian Mineralogist, 49, 117–136. [2] T. Setkova, Yu. Shapovalov, V. Balitsky (2011) Journal of Crystal Growth, 318, 904–907.

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1. Growth of Cr-containing topaz single crystals on a seed and their characterization