Abstract: Vivid blue inclusions in white whewellite or weddellite, occurring within the medulla of four lichen species growing on copper-bearing rocks, have been identified as the hydrated copper oxalate, moolooite, CuC₂O₄. nH₂O (n ∼ 0.4–0.7), by infrared spectroscopy and X-ray powder diffraction. The mineral is believed to have been formed by reaction between oxalic acid secreted by the lichen and ground or surface water containing copper.