KhALSEDON (az nomi shahri qadimii Khalkedon — Shalkedon dar sohili bahri Marmar), mineral, navi nimshaffof va mikrokristallii kvars. Dar tarkibash omekhtahoya Ge3+, A13+, to 1—1,5% ob va gayra dorad. Sokhtash nakhdor. Rangash safed, khokistari, bur, kabud, sabz, zardcha, surkhcha va gayra.
Bazan rakh-rakh, dogdor yo naqshdor meshavad. Xalsedon minerali bisyor pahnshudai jinsofarin buda, on az mahlulhoy gidrotermalii pastharorat, inchushin dar nroseoshoi diagenez, epigenez va farsoish paydo meshavad. Baze namudhoi khalsedon (aqiq. jaz, khrizolraz, salfirin va gayra) hamchun sangi oroishi az zamonhon khele qadim malum ast. Holo khalsedonro dar zargari baroi tayyor qardani asbobhoi daqiq ba kor mebarand.