Zircon's hardness makes it useful as an abrasive and it has a high melting point (over 2500°C), so it is used in the steel industry, to line furnaces. Zircon contains the metals zirconium and hafnium. Zirconium is extremely hard and resistant to corrosion so is used to make pipes for harsh chemicals, nuclear reactor cladding, heat exchangers and speciality alloys. Zirconium is found in computer disc drives, in lightweight clothing and in many domestic products such as ballpoint pens and wear-resistant knives. Hafnium is used in nuclear control rods and super alloys. Zircon products are also used in engines, electronics, spacecraft and the ceramics industry.