Garnet is a key mineral of several metamorphic and igneous rock types in the lithosphere. Despite being traditionally considered the archetypal cubic mineral, crystallizing in Ia $$\:\overline{3}$$ d space group, there is increasing evidence that almandine and spessartine garnets from low-temperature metapelites and metabasites are optically anisotropic, and therefore possibly not cubic. Here, we study the best-known occurrenc...