The Great Barrier Reef Expedition 1928-29: The crystal structure and occurrence of weddellite, ideally CaC2O4 center dot 2.5H(2)O, from the Low Isles, Queensland

摘要

"Envelope crystals" collected during The Great Barrier Reef Expedition in May 1929 have been studied using low-temperature synchrotron single-crystal X-ray diffraction. The crystals are shown to be weddellite, with the largest content of zeolitic water reported to date. A new H2O site has been located within the crystal structure. Study of the crystals show that the end-member formula for weddellite should be reported as CaC2O4 center dot(2.5 - x) H2O, where 0 <= x <= 0.25, instead of CaC2O4 center dot 2H(2)O or CaC2O4 center dot(2 + x) H2O. This is also the first report of weddellite occurring in a coral reef.