steacyite

{{Infobox mineral | name = Steacyite | image = Steacyite.jpg | alt = | caption = Steacyite crystals from the type locality of Mont-Saint-Hilaire, Quebec | category = Cyclosilicate | formula = {{chem2|K_{variable}(Ca,Na)2(Th,U)Si8O20}} | IMAsymbol = Scy | molweight = | strunz = 9.CH.10 | system = Tetragonal | class = Ditetragonal dipyramidal (4/mmm) H-M symbol: (4/m 2/m 2/m) | symmetry = P4/mcc | unit cell = | color = Gray, dark brown, green, beige | colour = | habit = | twinning = | cleavage = | fracture = | tenacity = | mohs = 5 | luster = Vitreous, greasy, dull | streak = | diaphaneity = Translucent, opaque | gravity = | density = | polish = | opticalprop = | refractive = | birefringence = | pleochroism = | 2V = | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = | impurities = | alteration = | other = 25px Radioactive | prop1 = | prop1text = | references = }}

Steacyite is a complex silicate mineral containing thorium and uranium; formula {{chem2|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.