Thermal expansion of fluorapophyllite KCa4[Si8O20]F • 8H2O in the 323-473 K range from X-ray powder diffraction data

Thermal expansion of fluorapophyllite KCa4[Si8O20]F • 8H2O has been analysed in the 323-473 K thermal range by laboratory parallel-beam transmission X-ray powder diffraction. Thermal expansion is markedly anisotropic as indicated by the α ̅_a of 2.205(13) • 10-5 and the α ̅_c of 4.98(15) • 10-6. Very minor variations of relevant bond distances are observed during heating. Anisotropy of thermal expansion has been attributed to the fact that the mean plane passing through Ca,O(4),K has a prevalent component along the (001)