Dice and other similar chips are made of cheap, slippery plastic, incosistent color-wise and even width-wise.
To give them some weight, a metal slug is placed inside them, resulting in their sounding like medieval chain armour.
Of course, they are almost indestructible, like any plastic thing.
The weight is actually too much at 11.5g (or even 14.5g in worse cases).
"American clay" compression mold chips (which are still to a high degree high-end plastics with some metal flakes) weigh 8-9g and used to weigh 10-10.5g when the flakes were made of lead (in the past).