SYNTHESIS OF THE SODALITE GROUP AND SUBSOLIDUS EQUILIBRIA IN THE SODALITE-NOSELITE SYSTEM

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The main end members of the sodalite group, that is, chlorine sodalite, bromine sodalite, iodine sodalite, hydroxylsodalite, carbonate noselite, sulfate noselite, chromate noselite, molybdate noselite and tungstate noselite, were synthesized under hydrothermal and dry conditions, and the cell edges a_o and cell volumes V of these minerals were determined. These minerals can be divided into two subgroups: the sodalite subgroup, which includes chlorine sodalite, bromine sodalite, iodine sodalite and hydroxylsodalite, and the noselite subgroup, which includes carbonate noselite, sulfate noselite, chromate noselite, molybdate noselite and tungstate noselite. The X-ray powder diffraction patterns of the four end members of the sodalite subgroup make their appearance only as h+k+l=2n. Those of five other end members which belong to the noselite subgroup appear as h+k+l=2n and h+k+l=2n+1.
The dissociation temperatures of chlorine sodalite and sulfate noselite are 1230°±5°C in chlorine sodalite and 1255°±5°C in sulfate noselite, and complete solid solution was found to exist between chlorine sodalite (Na₈Al₆Si₆O₂₄Cl₂) and sulfate noselite (Na₈Al₆Si₆O₂₄SO₄) at temperatures above 1050°C. Compositions of the chlorine sodalite-sulfate noselite solid solutions were determined from the cell edges a_o, obtained by measuring the shifts of the 211, 310 and 222 reflections (CuKα). A solvus of the chlorine sodalite-sulfate noselite series was determined at temperatures below 1050°C. Polymorphic relationship was discovered in the sulfate noselite in the noselite subgroup.