Introduction: Hydrated magnesium sulfate minerals, such as kieserite (MgSO4·H2O), hexahydrite (MgSO4·6H2O), epsomite (MgSO4·7H2O), and meridianiite (MgSO4·11H2O) are likely to be important planetary materials. On the icy moons, these hydrated phases have been suggested as possible non-water phases at the surface [e.g. 1,2,3], and may affect the possibility and rate of solid-state convection within the interiors. On Mars, meridianiite, hereafter called MS11, may be the most abundant hydrate mineral on the planet, and is important in studies of the present martian water budget [4]. The aim of this study is to expand the limited knowledge of the strength of hydrated magnesium sulfates, and MS11 in particular.