a dense silvery-white metallic element that has a high melting point. It occurs principally in gadolinite and molybdenite and is used, alloyed with tungsten or molybdenum, in high-temperature thermocouples. Symbol: Re; atomic no: 75; atomic wt: 186.207; valency: –1 or 1–7; relative density: 21.02; melting pt: 3186°C; boiling pt: 5596°C (est)