As obtained by Moissan in the fused condition by means of an electric furnace, although not quite free from carbon, metallic titanium is not unlike silicon, but whiter, lustrous, very hard, but brittle, of specific gravity 4.87. It burns when heated in the air, and is attacked by the common mineral acids, a light strong grey lustrous corrosion-resistant metallic element used in strong lightweight alloys (as for airplane parts); the main sources are rutile and ilmenite, A chemical element, atomic number 22; it is a strong, corrosion-resistant transition metal, used to make light alloys for aircraft etc.