Crystal data for calcium fluoride silicon oxide (CaF₂.SiO₂), a dehydration product of fluorapophyllite

Powder data for a previously unreported dehydration product of fluorapophyllite (KCa₄Si₈O₂₀F.8H₂O) are presented. The reflexions are indexed on the basis of a tetragonal cell with a = 6.937 ± 0.003 and c = 8.488 ± 0.004 Å, (c/a = 1.2235 ± 0.0008). The d spacings and intensities correspond to the unindexed data for CaF₂.SiO₂ in the JCPDS file (Card No. 20-1050) and the refined cell dimensions are identical, to within the experimental error. Single-crystal data have not yet been obtained for this phase.