The Chemistry of Snowflakes

[n2doc]

[littlemissmartypants]

1. Thank you. n/t

[niyad]

2. k and r

[struggle4progress]

3. OK. Who wants to tackle the approximate 6-fold symmetry of the complex flake?

The 6-fold symmetry of a hexagon isn't mysterious, of course, but each water molecule gets added at one plane, not at six or twelve places. So one might understand a snowflake that grew without much global symmetry, as a number of partial hexagons stuck together. But since there's no obvious reason a defect or irregularity on one face of a hexagon should be duplicated on the other faces, there's no obvious reason any snowflake's particular shape should be symmetric

So, obviously, it has something to do with the thermodynamics of the situation, and perhaps the accuracy of snowflake symmetry should be affected by factors such as (1) how saturated the air is with moisture; (2) the rate which the snowflake grows; (3) how long the snowflake grows; and so on. But it might also be affected by the size and approximate symmetry of the mote that formed the original condensation nucleus

[Jim__]

4. According to wikipedia, they're not exactly symmetric.

From wikipedia:

A non-aggregated snowflake often exhibits six-fold radial symmetry. The initial symmetry can occur[12] because the crystalline structure of ice is six-fold. The six "arms" of the snowflake, or dendrites, then grow independently, and each side of each arm grows independently. Most snowflakes are not completely symmetric. The micro-environment in which the snowflake grows changes dynamically as the snowflake falls through the cloud, and tiny changes in temperature and humidity affect the way in which water molecules attach to the snowflake. Since the micro-environment (and its changes) are very nearly identical around the snowflake, each arm can grow in nearly the same way. However, being in the same micro-environment does not guarantee that each arm grows the same; indeed, for some crystal forms it does not because the underlying crystal growth mechanism also affects how fast each surface region of a crystal grows.[13]

[struggle4progress]

5. I did write: "approximate 6-fold symmetry"

[Jim__]

6. Right. The microenvironment explains the approximate symmetry.

... Since the micro-environment (and its changes) are very nearly identical around the snowflake, each arm can grow in nearly the same way. ...