Among the extremely valuable donations made to thethe Mining Institute Museum, is a specimen of pseudo-crystals of enormous size, currently composed primarily of malachite. From this specimen, it was possible to extract small tabular pseudomorphs that perfectly preserved their original form, partly even with mirror-like, lustrous faces. Due to this circumstance, the method of crystal chemical analysis could be applied with exceptional clarity, allowing it to be established with full certainty that these were pseudomorphs of atacamite. Using the tables of crystal chemical analysis, the entire series of substances was revised according to the symbol closest to that obtained from an approximate measurement, and identity in form was found for only for one substance, namely atacamite. These findings are presented in this note.