Frost, Hexagons, Ice, Life

Frost image by Sandy Robertson.

"We had a couple of days of hard frosts and there were some wonderful growths of small ice crystals on the shed roof.

What amazed me was the clarity of the hexagonal shape of some of the crystals and the way that they built up in layers (stacked plates). This really brought home to me how water can form hexagonal crystals.

I always find that however much one hears and 'understands' the theory, seeing a phenomenon in the flesh so to speak can add an extra level of appreciation........ and apart from that, I thought they looked really pretty in their own right!

The photo was taken under natural light (shadow, but blue sky) using a reversed lens (50mm) attached to the front of the main lens (18-55mm). It is a low cost way to get macro capability.

©Sandy Robertson, shown with permission

Two sights that we would not see but for the open hexagonal structure of ice.

Ice halos (Tom Faber) and icebergs (Les Cowley).
Atmospheric
Optics
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Ice crystals, from simple columns and plates that make halos to the intricate structures of frost and snowflakes, are all hexagonal in form. Their six-sidedness is a direct manifestation of ice�s molecular structure for that too is strongly hexagonal.

Ice�s hexagonal arrangement at a molecular level is a consequence of highly directional bonding between oxygen and hydrogen atoms combined with additional �hydrogen bonding�. The hydrogen bonding � an extra electrostatic interaction between an already bonded hydrogen atom and the oxygen of an adjacent water molecule � helps produce an uncommonly open and low density crystal lattice as the most stable ice form at everyday temperatures and pressures.

The low density has far reaching consequences. Ice is almost unique in that it floats on its own liquid � water. Nearly all other solids sink in their liquid form.

Earth would be quite different if ice did the same. Floating ice prevents shallow water from freezing completely in winter making aquatic life difficult or impossible. Worse, the overall energy balance of the planet would be different and life as we know it probably nonexistent.

Plus halos would have rather different shapes!
Ball and stick model of the molecular structure of ice. Red balls are oxygen atoms. Hydrogen atoms are between them along the white sticks but are not equidistant. Two hydrogen atoms are bonded strongly (covalently) to one oxygen atom and more loosely via 'hydrogen bonding' to an adjacent oxygen. The result is an unusually open, hexagonal, structure..