Why triangular snowflakes grow

While most snowflakes are hexagonal, triangular forms have long been observed. When Libbrecht and Arnold grew snow crystals in the lab they found far more triangular forms than would be expected from mere random growth perturbations.

Air moving past a falling crystal will increase its growth, they note. A tiny factor – perhaps a piece of dust on the crystal – that causes a small change in growth of a perfect hexagon will also tilt the crystal, changing the way air moves past the crystal and – in their model – increasing the way the crystal grows at certain points and inducing a more triangular appearance.

Also: Unusual Snow Crystals. Be sure to check out the photo galleries.

Update: and The Unbelievable World of Snowflakes