Evidence for the recently described 2M2 polytype of brochantite from X-ray powder diffraction investigation of secondary alteration products of ore material from the Pierre Plate Mine, Vizille, Isère, France is presented. This report is the first to describe the 2M2 polytype from locations outside of Italy and through the use of powder XRD methods. In the procedure used herein, developed in a study by Merlino et al. [Eur. J. Mineral 15, 267–275 (2003)], we have used family reflections, common to both main types of brochantite, as the source of approximate cell parameters from which we obtain positions of characteristic reflections to demonstrate the unique choice of polytype, before final refinement stage. This method demonstrates that the determination of polytype is possible from powder data, for samples typical of both geological and urban environments. Least-squares refined cell parameters for the 2M2 polytype from Pierre Plate are a=12.7409(8) Å, b=9.8371(6) Å, c=6.0109(3) Å, and a=90.135(9)°, constrained in space group P21/n11.