First Record of Erythrite (Co₃(AsO₄)₂·8H₂O) in Huaytapallana, Peru: Mineralogical Reclassification of Previously Reported Garnet Occurrences

Erythrite (Co₃(AsO₄)₂·8H₂O) is a secondary cobalt arsenate mineral commonly associated with hydrothermal and supergene environments, yet its occurrence in high-grade metamorphic terrains remains poorly documented. This study reports the first confirmed occurrence of erythrite in the Huaytapallana area, central Peru, where it was previously misidentified as garnet in regional petrographic descriptions. Two representative samples were analyzed through detailed macroscopic observation and transmitted-light petrography.The host rocks correspond to quartz-feldspar-biotite gneisses affected by regional metamorphism, displaying granolepidoblastic to porphyroblastic textures. In both samples, erythrite occurs as anhedral to subhedral blastos and porphyroblasts, locally fractured, hosting inclusions of quartz, apatite, zircon, sillimanite, and opaque minerals. Textural relationships indicate that erythrite postdates the main metamorphic mineral assemblage and is spatially associated with microfractures, oxidation features, and incipient alteration processes, suggesting a late-stage formation under post-metamorphic conditions.The mineralogical reclassification presented here corrects earlier interpretations that attributed the reddish-pink mineral phases to garnet. This revision has direct implications for regional metamorphic mapping and for understanding cobalt mobility in polymetamorphic terrains. The results highlight the importance of detailed petrographic analysis to avoid systematic misidentification of visually similar minerals in metamorphic environments. Keywords: erythrite, Huaytapallana, mineralogical reclassification, metamorphic gneiss, cobalt arsenates.