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Six arms, one journey

Why Is Every Snowflake Different?

A snowflake's shape is a record of every temperature it fell through.

One flake from thesky Water molecules lockedin a six-sided grid
The six arms come from the shape of ice itself.

  1. Step 1 of 5

    Ice always builds a six-sided grid.

    Any piece of ice Bent molecules that onlyfit one way

    Water molecules are bent, and when they lock together they can only stack in a honeycomb pattern. That hexagon is fixed by the molecule, not by chance.

  2. Step 2 of 5

    Growth starts on a speck of dust.

    1 A speck of dust2 Water freezesonto it3 Six arms growoutward

    A flake needs something to begin on. A grain of dust or pollen gives the first molecules somewhere to land, and the crystal spreads outward from there.

  3. Step 3 of 5

    Corners grow fastest.

    A tiny hexagon Arms racingoutward from thecornersWhatever sticks out, grows fastest

    The six corners stick out furthest into the vapour, so they collect molecules first. That is why arms shoot out instead of the flake growing as a fat lump.

  4. Step 4 of 5

    Temperature changes the style of arm.

    −2 °C — thin platesflat and simple−5 °C — needleslong and spiky−15 °C — lacy starsthe classicsnowflake

    Near minus two degrees ice grows flat plates. Near minus fifteen it grows lacy stars. The flake switches style every time it drifts through a different layer.

  5. Step 5 of 5

    All six arms take the same journey.

    Within one flake Same journey — sixmatching armsBetween two flakes Different paths —different shapes

    The arms are only a millimetre apart, so they meet identical air at identical moments and grow alike. Two different flakes never take the same path.

    A cubic metre of fresh snow holds roughly a hundred million flakes, which is why nobody has ever checked the claim properly.

The short version

Ice can only grow six ways, but each flake's exact path through the cloud gives it a shape no other flake has.

Try it yourself

Catch flakes on a cold dark sleeve and look with a magnifier. On the same day they will all share a family style.

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