His discovery of coesite, which became a standard sign of an impact crater, sealed the debate.

ECONOMIST: Gene Shoemaker

Coesite is a variant of quartz that forms only under intense heat and pressure.

ECONOMIST: Gene Shoemaker

To his delight, the stones contained coesite, a mineral he had found a year earlier in the 1, 200-metre-wide Barringer crater in Arizona, near his home.

ECONOMIST: Gene Shoemaker