Agardite (Ce) is a member of the mixite group (complex copper based arsenates and phosphates) with the formula CeCu6(AsO4)3(OH)6 3H2O. It forms acicular, pistachio-green crystals that are typically found in tiny tufts. All photographed specimen originate from the Clara mine, Oberwolfach in Germany.
The artistic picture shows the crystal structure along the c-axis using the data from Hess (Neues Jahrbuch für Mineralogie 1983 (1983) 385). Cerium atoms (yellow) are surrounded by distorted arsenate tetrahedra (green) and square-pyramidal coordinated copper (blue). The channels are hosting water molecules, symbolized as white-red dots. Nota bene that the real composition is more complex with smaller portions of Ca, Fe(III), Cu and Mn sharing the Ce sites and Sb occupying some As sites. This has recently been reported together with a refined crystal structure by Aksenov et al. (Phys. Chem. Minerals 45 (2017) 39).