Niobium has a density of 8.57g/cm³, a melting point of 2,477 °C and a boiling point of 4,744 °C. Niobium is a silver-gray, soft and malleable rare high melting point metal. At room temperature, niobium does not react with air and will not be completely oxidized when red hot in oxygen. Niobium can combine directly with sulfur, nitrogen and carbon at high temperature. Niobium does not react with inorganic acids or bases and is insoluble in aqua regia, but soluble in hydrofluoric acid.