In pure form at 24Kt, gold is very soft and easily malleable. Mixed with other metals, like silver or copper, alloyed gold is harder and less expensive.
The scientific abbreviation of gold is Au. Karats refer to the measurement of pure gold in jewellery. Some countries brand gold with a three-digit number that indicates the parts per thousand of gold. For example, "750" means 750/1000 gold (equal to 18K); "585" means 585/1000 gold (equal to 14KT).
Platinum is the strongest, most pure metal. Platinum jewellery is composed of 90-95% pure platinum. Rarer than gold, platinum is up to three times the price of gold. Resistant to damage and wear, it will last a lifetime. Platinum jewellery develops a satin finish. It doesn't require much care as it will not tarnish. It is however, difficult to polish and repair.