HIGH-TEMPERATURE REACTIONS OF ALKALI AND PLAGIOCLASE FELDSPARS WITH ALKALI AND ALKALINE-EARTH CHLORIDES - FORMATION OF CELSIAN

High-temperature reactions (Ca 900-degrees-C) involving albite, K-feld spar or plagioclase and K, Ba-or K, Sr chlorides were experimentally s tudied. These experiments reveal that the reaction between K-exchanged albite, potash feldspar, or plagioclase and Ba-chloride/Ba-K chloride results in the formation of celsian by the breakdown of the starting feldspar structure above 800-degrees-C. Sr-feldspar does not form unde r similar conditions. A size-effect of the large M-site cation appears to be responsible for the formation of celsian. The reaction between K-feldspar and barium chloride may be used as a method for synthesizin g celsian.