gold you can carry in a backpack on your dirtbike as you flee the conflagration and riots. Coal, no so much. Diamonds are not clearly valued. Copper, too heavy.

gold was illegal in the USA 1955, but americans had lots of it stashed away. and you could buy things with it. always. as long as man is on the planet.

pretty good track record as a store of value. sure it varies, like anything, but it will never ever ever go to zero. and in general, 1 oz will buy a few hundred loaves of bread.