Most individual snow crystals have a six-sided foundation because water molecules arrange themselves in a hexagonal pattern when they freeze. As water vapor builds up on a falling crystal, six corners may grow outward into the familiar six arms. Not every real snowflake looks like a perfectly balanced star; many are simple plates, columns, needles or clumps of crystals.
Why six sides instead of five or eight?
A water molecule is made of two hydrogen atoms and one oxygen atom. When many molecules freeze into ordinary atmospheric ice, hydrogen bonds help organize them into a hexagonal crystal lattice. This arrangement produces sixfold symmetry in the growing crystal. The six-sided design is built into the structure of the ice rather than chosen by the wind or by how fast the snow falls.
NOAA’s illustrated classroom guide explains the two basic kinds of snow-crystal growth: flat facets and branching arms.
See the sixfold pattern in a real snowflake
Look closely at this macro photograph of a star-shaped snow crystal. There is a hexagonal center, with six short, broad arms arranged around it. Each branch has fine details that were formed as water vapor condensed and froze onto the crystal.
Why do some snowflakes grow long delicate branches?
At first a crystal may be a tiny hexagonal plate. Corners can catch water vapor more effectively than flatter edges, encouraging growth from six directions. As tips lengthen, they can develop side branches, producing fern-like patterns known as dendrites. Crystal growth depends on the temperature and available water vapor in the cloud. A high-humidity environment may favor branches; under other conditions, simple plates or columns form instead.
Why do the six arms usually look so similar?
They grow very close together, so the six arms usually encounter nearly the same changing temperatures and humidity. That shared history often produces a repeating design. But small local differences matter, so the arms of natural snowflakes are rarely perfectly identical. The symmetry is an overall pattern, not evidence that snow crystals were assembled from identical pieces.
Does every snowflake really have six points?
No. The basic ice-crystal structure is hexagonal, but a snowflake falling to the ground can be broken, partially melted, stuck to another crystal, or shaped like a column or plate instead of a star. Some crystals appear triangular; under special circumstances, crystals with more than six visible points can form. Photos of perfect stars show just one especially striking class of snow crystal.
Why aren’t two snowflakes exactly the same?
Each crystal drifts through its own sequence of cloud conditions, including temperature, humidity and collisions. Tiny differences at each growth stage create enormous variation in the final details. It is not impossible for small simple crystals to look almost identical, but finding two complicated branched snowflakes with every feature matching would be extraordinarily unlikely.
A family activity: make a paper snowflake with six arms
Start with a square sheet of thin paper. Fold it in half diagonally to make a triangle; fold that triangle in half, then fold its point into three approximately equal wedges to create sixfold symmetry when unfolded. Trim the uneven top edge and cut small notches along the folded sides, keeping a connected strip of paper so it does not fall apart. Carefully unfold to see a six-sided design. Adults should supervise scissors. A paper version is a model, not a microscopic replica of ice crystal growth.
Frequently asked questions
Are snowflakes made from frozen raindrops?
Usually they form as ice crystals growing from water vapor in cold clouds. Frozen raindrops are a different kind of precipitation particle, such as sleet.
Can snowflakes have twelve arms?
Unusual joined crystals can appear to have twelve branches, but each component still reflects the underlying hexagonal ice symmetry.
What makes a snowflake become a needle instead of a star?
Temperature and humidity during growth help determine whether an ice crystal develops plates, needles, columns or branching designs.
Why does snow look white if ice is clear?
Many tiny crystal surfaces scatter light in different directions; a mass of snow looks white even though an individual snow crystal may be transparent.
Related reading: How snow forms inside clouds. For more examples, see NOAA’s explanation of snow-crystal shapes.
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