A Preliminary Study on "Heidan" Stone

A kind of so-called "Heidan" stone is appeared in Beijing jewelry markets.It is black and has strong magnetism,which is called "hematite" or "goethite" by traders.The stone samples are preliminarily studied by using the conventional gemmological tests and advanced equipments in order to get the correct name.The results show that the samples are mainly composed of Fe and Sr,and the chemical composition is SrO·6Fe₂O₃.So the stone is inferred an artificial magnetic material——strontium ferrite,but not hematite or goethite.