Atoms joining a queue
How Do Crystals Grow?
Crystals grow when atoms leave a liquid and lock onto a repeating pattern.
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Step 1 of 5
A liquid can only hold so much.
Dissolved substance stays put while there is room. Once the liquid is saturated, anything extra must come out as solid.
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Step 2 of 5
Atoms attach in a specific arrangement.
Each atom fits onto the growing solid in only certain positions, determined by its shape and charge. That pattern repeats indefinitely.
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Step 3 of 5
That is why crystals have flat faces.
A repeating internal pattern produces flat outer surfaces at fixed angles. Salt makes cubes because its atoms stack in cubes.
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Step 4 of 5
Slow growth makes bigger crystals.
Patience is not a technique here. It is the only variable that matters. Rapid cooling starts millions of tiny crystals at once. Slow cooling lets a few grow large, which is why patient methods give better results.
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Step 5 of 5
It happens in nature the same way.
Mineral-rich water slowly evaporating or cooling in rock cavities grows crystals over thousands of years — sometimes metres long.
A cave in Mexico holds gypsum crystals over ten metres long, grown in warm mineral water over half a million years.
The short version
Atoms can only attach in certain positions, so the repeating pattern inside shows up as flat faces outside — salt makes cubes because its atoms stack in cubes. Slow cooling is the only thing that makes them big.
Try it yourself
Dissolve as much salt as you can in hot water and hang a string in it. Crystals grow on the string over days.