Usually, when the crystals are cold, these atoms don’t have enough energy to move around and do something about their predicament. But when the temperature is high enough, the atoms can move around: they set about reorganizing themselves so that as few of them as possible are forced to inhabit a position at the surface of the crystal—so that, in fact, there is less surface overall. In doing so, they reshape the crystals to fit together as fully and economically as possible, eliminating the holes between them. Slowly but surely the collection of tiny crystals become a single material. It’s not
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