The crystal structure of waylandite from Wheal Remfry, Cornwall, United Kingdom

Sr- and Ca-rich waylandite, $ {left( {{hbox{B}}{{hbox{i}}_{0.{54}}}{hbox{S}}{{hbox{r}}_{0.{31}}}{hbox{C}}{{hbox{a}}_{0.{25}}}{{hbox{K}}_{0.0{1}}}{hbox{B}}{{hbox{a}}_{0.0{1}}}} right)_{Sigma 1.12}}{{hbox{H}}_{0.{18}}}{left( {{hbox{A}}{{hbox{l}}_{{2}.{96}}}{hbox{C}}{{hbox{u}}_{0.0{2}}}} right)_{Sigma 2.98}}{left[ {{{left( {{{hbox{P}}_{0.{97}}}{{hbox{S}}_{0.0{3}}}{hbox{S}}{{hbox{i}}_{0.0{1}}}} right)}_{Sigma 1.00}}{{hbox{O}}_4}} right]_2}{left( {hbox{OH}} right)_6} $ , from Wheal Remfry, Cornwall, United Kingdom has been investigated by single-crystal X-ray diffraction and electron microprobe analyses. Waylandite crystallises in space group R $ overline 3 $ ? m, with the cell parameters: a?=?7.0059(7) Å, c?=?16.3431(12) Å and V?=?694.69(11) ų. The crystal structure has been refined to R ₁?=?3.76%. Waylandite has an alunite-type structure comprised of a rhombohedral stacking of (001) composite layers of corner-shared AlO₆ octahedra and PO₄ tetrahedra, with (Bi,Sr,Ca) atoms occupying icosahedrally coordinated sites between the layers.