a hard grey metallic element that takes a high polish, occurring principally in chromite: used in steel alloys and electroplating to increase hardness and corrosion-resistance. Symbol: Cr; atomic no: 24; atomic wt: 51.9961; valency: 2, 3, or 6; relative density: 7.18–7.20; melting pt: 1863±20°C; boiling pt: 2672°C