Malachite pseudomorph after cuprite showing octagon and dodecahedron faces. From Chessy, France. Specimen is just over 1 cm in maximum dimension. Photo by Richard I. Gibson.Today for Mineral Monday my special guest is Kyle Eastman, mineral collector and geologist, here to discuss with me some special minerals called pseudomorphs. These are “false form” minerals that have the shape of one mineral but are actually something else because of replacement, substitution, encrustation, or some other process. We discuss some classic pseudos from Chessy, France and Corocoro, Bolivia, as well as one of Kyle’s favorite skarns from Arizona. Running time, 19 minutes. —Richard I. Gibson