Marie-Clotilde-Elisabeth Louise de Riquet (3 June 1837 – 8 November 1890) known as Louisa de Mercy-Argenteau, was a Belgian pianist. She was the eldest daughter of Michel Gabriel Alphonse Ferdinand de Riquet (1810–1865), created prince de Chimay 1834, for himself only, and Rosalie de Riquet de Caraman (1814–1872)