English: (a) Richardsite coating a wurtzite–sphalerite crystal cluster with oriented terraces of secondary sphalerite crystals (not coated by richardsite). Minor diopside is present at the lower right. (b) Nearly parallel growth of richardsite crystals showing disphenoidal forms with stepped surfaces. (c,d) Apparent epitaxic overgrowth of richardsite on selective facets of primary wurtzite–sphalerite crystals. The image is published in an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).