Ekanite is an uncommon silicate mineral with chemical formula Ca2ThSi8O20 or (Ca,Fe,Pb)2(Th,U)Si8O20. It is a member of the steacyite group. It is among the few gemstones that are naturally radioactive. Most ekanite is mined in Sri Lanka, although deposits also occur in Russia and North America. Clear and well-colored stones are rare as the radioactivity tends to degrade the crystal matrix over time in a process known as metamictization.