Put a piece of quartz under an electron microscope and it will shine an icy blue. First noticed in the 1960s, the phenomenon, called cathodoluminescence, gave geologists an easy way to identify quartz and other minerals in rock samples. But the light -- emitted after a beam of electrons kicks a material’s own electrons into a higher-energy state -- is faint and diffuse, and that discouraged other scientists from harnessing it for fine-scale imaging.
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