Synthesis and characterization of [K.sub.2][Ca.sub.5][(S[O.sub.4]).sub.6]*[H.sub.2]O, the equivalent of gorgeyite, a rare evaporite mineral

Gorgeyite, [K.sub.2][Ca.sub.5][(S[O.sub.4]).sub.6]*[H.sub.2]O, is a very rare monoclinic double salt found in evaporites related to the more common mineral syngenite. At 1 atmosphere with increasing external temperature from 25 to 150[degrees]C, the following succession of minerals was formed: first gypsum and [K.sub.2]O, followed at 100[degrees]C by gorgeyite. Changes in concentration at 150[degrees]C due to evaporation resulted in the formation of syngenite and finally arcanite. Under hydrothermal conditions, the succession is syngenite at 50[degrees]C, followed by gorgyeite at 100 and 150[degrees]C. Increasing the synthesis time at 100[degrees]C and 1 atmosphere showed that initially gypsum was formed, later being replaced by gorgeyite. Finally gorgeyite was replaced by syngenite, indicating that gorgeyite is a metastable phase under these conditions. Under hydrothermal conditions, syngenite plus a small amount of gypsum was formed, after two days being replaced by gorgeyite. No further changes were observed with increasing time. Pure gorgeyite showed elongated crystals approximately 500 to 1000 [micro]m in length. The infrared and Raman spectra are mainly showing the vibrational modes of the sulfate groups and the crystal water (structural water). Water is characterized by OH-stretching modes at 3526 and 3577 [cm.sup.-1], OH-bending modes at 1615 and 1647 [cm.sup.-1], and an OH-libration mode at 876 [cm.sup.-1]. The sulfate [v.sub.1] mode is weak in the infrared but showed strong bands at 1005 and 1013 [cm.sup.-1] in the Raman spectrum. The [v.sub.2] mode also showed strong bands in the Raman spectrum at 433, 440, 457, and 480 [cm.sup.-1]. The [v.sub.3] mode is characterized by a complex set of bands in both infrared and Raman spectra around 1150 [cm.sup.-1], whereas [v.sub.4] is found at 650 [cm.sup.-1].