Abstract: Margarite occurs in Ordovician black slate within the contact aureole of the Wyangala Batholith, in the Lachlan Fold Belt in New South Wales. This occurrence is the first described from New South Wales. It is a regional metamorphic mineral replacing chiastolitic andalusite, and contains up to 1.07% V₂O₃ and up to 0.37% Cr₂O₃. Vanadium and chromium here substitute for octahedral aluminium. Margarite is produced by a local reaction in which Ca and H₂O are introduced into andalusite grains. There is a significant paragonite component in the margarite but negligible muscovite solid solution.