Diamonds are hard beyond belief. Of the 100 million or so carats mined each year, those in the very top grade number in the hundreds. What's more, about half of a rough diamond's total weight is lost in the cutting process. Diamonds personify value. The luxury car, the private plane, the regal fur are all passing pleasures.
Diamonds are forever.
Diamonds have an affinity for grease and literally collect oils in dishwater. Diamonds are also susceptible to damage from an impact that might cause them to chip or crack.