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{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}

| 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.{{cite journal |last1=Dunn |first1=P.J. |last2=Fleischer |first2=M. |last3=Burns |first3=R.G. |last4=Pabst |first4=A. |title=New mineral names |journal=American Mineralogist |date=1983 |volume=68 |pages=471–000 |url=http://www.minsocam.org/ammin/AM68/AM68_471.pdf |access-date=14 March 2022}}