In 1961, three prospectors in California found a sparkplug encased in solid rock.

It was originally thought to be 500,000 years old, which would put it in a class with the Kingoodie Hammer and the Dorchester Pot.

More recent investigations say the “rock” is just a concretion of iron oxide produced by the rusting plug, which may date only from the 1920s … but discoverer Mike Mikesell says he destroyed a diamond-edged blade in cutting through it.