Steacyite is a complex silicate mineral containing thorium and uranium; formula K_variable(Ca,Na)₂(Th,U)Si₈O₂₀. It forms small brown or yellow green crystals, often cruciform twinned crystals. It is radioactive. It was discovered at Mont-Saint-Hilaire, Quebec in 1982 and is named after Harold Robert Steacy (1923-2012), mineralogist.