La Espátula Roja: December 2010

Snow crystal shapes depend on the temperature and humidity.
Thin plates and stars grow around -2 C (28 F), while columns and slender needles appear near -5 C (23 F). Plates and stars again form near -15 C (5 F), and a combination of plates and columns are made around -30 C (-22 F).

Why snow crystal shapes change so much with temperature remains something of a scientific mystery. The growth depends on exactly how water vapor molecules are incorporated into the growing ice crystal, and the physics behind this is complex and not well understood.

If you look closely at falling snow, you can see a great many different crystal shapes. There's a lot more to see than you might think!

click to enlarge

Photography by spirithelpers

When water freezes into ice, the water molecules stack together to form a regular crystalline lattice, and the ice lattice has six-fold symmetry. It is this hexagonal crystal symmetry that ultimately determines the symmetry of snow crystals.