The requirements for being truly called a “precious stone” are incredibly strict – basically, if a stone is not an emerald, ruby, sapphire or diamond, it is out of luck. The diamond, however, is the king of the heap when it comes to this extremely select company. The first stone that springs to one’s mind in any valuable context, it is the quintessential precious object, even before the memories that inevitably accrue to a gem so often given as a sign of earnest affection.