How is the shape of a snowflake determined?

Question

And how are the formed so symetricly?

Answer 1

Randomness

Answer 2

Elements, and most minerals, have specific crystallisation patterns. H2O, in solid form, if crystallised from water vapour....

Let me back up. All elements, and many mineral compounds (which, weirdly enough, H2O is -- well, it's not vegetable or animal!) can occur in three states (that we know of): Solid, Liquid, or Gaseous.

Assuming perfect laboratory conditions for 'Earth Normal' -- Altitude=0, Latitude=0 -- 1cm²/ml of H2O becomes gaseous at 100° Celsius, and becomes solid at 0° Celsius -- H2O is most stable as a liquid, in most places on Earth. (This is true of all minerals and mineral compounds -- they tend to be more stable in one or another state at 'Earth Normal').

The higher you take water, in either latitude, or altitude, the colder the general conditions, so you have polar ice caps, and glaciers on mountain-ranges. Ice is H2O in its solid form.

The atmosphere of Earth grows less and less dense, the further away (higher) you get from sea-level, until eventually the Earth's gravity is simply not strong enough to hold the atmosphere in, and you are in Outer Space.

Anyone who has ever been in a 'plane knows that they fly above the clouds. Clouds are water vapour (H2O in its gaseous state).

The atmosphere is a very complex, mobile, constantly fluctuating system, affected by pretty much everything from the Sun, to cows breaking wind.

The crystalline structure of minerals and compounds is not something I have enough Chem to explain, but it has to do with the way different elements bond together, I think. Not all minerals crystallise (so far as I know), but some that do, that I can think of, offhand, are salt, which is cubic, sand (silica) which has triangular facets, and mica, which bonds in sheets.

Water vapour that is sufficiently cold, remains gaseous in the atmosphere (not solid, because of low density - don't worry about this unless you want to) until there is not enough 'room' for the H2O molecules to stay pressed up against each other. This is where the barometric and other atmospheric variables come in. But, we all know that clouds 'pile up' before storms.

The six-pointed, or six-branched structure of snow is most often seen on very dry, cold nights. This is called 'dry' snow. Warm air, trapped between the Earth and the clouds, causes the crystalline shape to melt. Humidity makes the crystals both melt, and stick together, creating much larger 'flakes', and what's called 'wet' snow. The speed with which the snow falls also affects the way the flakes end up, when they land.

Europe is not the best place (barring in the Alps) to see a really good dry snow. (Lots of unnecessary meteorology omitted because it's not relevant).

In short, the symmetry of any crystalline structure is a chemical property of that structure, and just IS that way. H2O, when freezing in particles, creates a flat, six-pointed shape.

That's its NATURE. It's a bit like asking why maple-leaves are maple-leaf shaped (only the answer to THAT would take flippin' hours to explain).

Now, the fact that H2O actually EXPANDS when it goes from liquid to solid form (NOTHING ELSE ON EARTH DOES THAT) is where my scientific knowledge goes all squinty, and slopes off for a cuppa. ROFL

Hope that answered your question, sort of.

Answer 3

If you are interested in snowflakes then 'About Grace' by Anthony Doerr is a fascinating book as the main character's obsession with snowflakes shines through.

In the book the reference section links to Wilson Bentley (whose website is here: http://snowflakebentley.com/) a man who himself was fascinated by snowflakes. His website is of interest to anybody interested in snowflakes and contains links including this one: http://www.its.caltech.edu/~atomic/snowcrystals/photos/photos.htm which answers your question and provides fantastic photographs of actual snowflakes.

The water molecules in an ice crystal form a hexagonal lattice. There are two hydrogens for each oxygen, so the chemical formula is H2O. The six-fold symmetry of snow crystals ultimately derives from the six-fold symmetry of the ice crystal lattice.

Answer 4

A snowflake usually has six symmetric arms (along three symmetric axes), which arise from the hexagonal crystal structure of ordinary ice along its 'basal' however, the exact shape of the snowflake is determined by the temperature at which it forms.[1]. Rarely, at a temperature of around -2 C (28 F), snowflakes can form in three-fold symmetry - triangular snowflakes.[2] Snowflakes are not perfectly symmetric however. The most common snowflakes are visually irregular, although near-perfect snowflakes may be more common in pictures because they are more visually appealing.

Snowflakes can come in many different forms, including columns, needles, and plates (with and without "dendrites" - the "arms" of some snowflakes). These different forms arise out of different temperatures and water saturation - among other conditions. Snowflakes form below about -10 C (14 F), solidifying around a frozen center droplet. Between temperatrues of -1 C (30 F) and -3 C (27 F), the snowflake will be in the form of a dendrite or a plate. As temperatures get colder, between -5 C and -10 C The crystals will form in either needles or hollow columns. In special circumstances, where the crystal has started forming at around -5 C, and is then exposed to warmer or colder temperatures, a capped column may be formed which consists of a column like design capped with a dendrite or plate like design on each end of the column. [1] At even colder temperatures, the snowflake design returns to the more common dendrite and plate. At temperatures approaching -20 C, Sectored plates are formed which appears as an dendrite, which each dendrite appearing flattened, like the design of an snowflake plate.[1]

Snow machines shoot a mixture of water and compressed air out of nozzles. The water comes out as fine droplets, and the air cools as it decompresses, causing the droplets to freeze. A fan blows the ice particles onto the slopes. Artificial snow is made of frozen water droplets, with none of the elaborate structure found in real snow crystals.

There are, broadly, two possible explanations for the symmetry of snowflakes. Firstly, there could be communication or information transfer between the arms, such that growth in each arm affects the growth in each other arm. Surface tension or phonons are among the ways that such communication could occur. The other explanation, which appears to be the prevalent view, is that the arms of a snowflake grow independently in an environment that is believed to be rapidly varying in temperature, humidity and other atmospheric conditions. This environment is believed to be relatively spatially homogeneous on the scale of a single flake, leading to the arms growing to a high level of visual similarity by responding in identical ways to identical conditions, much in the same way that unrelated trees respond to environmental changes by growing near-identical sets of tree rings. The difference in the environment in scales larger than a snowflake leads to the observed lack of correlation between the shapes of different snowflakes. The six-fold symmetry happens because of the basic hexagonal crystaline structure from which the snowflake grows. Surprisingly, the exact reason for the three-fold symmetry of triangular snowflakes is still a mystery.

There is a widely-held belief that no two snowflakes are alike, but that claim has not been proven, and, due to the astronomical number of snowflakes that fall, is impossible to prove by exhaustive methods. Strictly speaking, it is extremely unlikely for any two objects in the universe to contain an identical molecular structure; but, there are, nonetheless, no known scientific laws which prevent it. In a more pragmatic sense, it's more likely, albeit not much more, that two snowflakes are visually identical if their environments were similar enough, either because they grew very near one another, or simply by chance. The American Meteorological Society has reported that matching snow crystals were discovered by Nancy Knight of the National Center for Atmospheric Research. The crystals were not flakes in the usual sense but rather hollow hexagonal prisms.

A common estimate is that a snowflake can appear in 10158 forms, under the estimate that a snowflake has 100 attributes which can vary, resulting in 100! forms. However, the number of possible snowflakes per the atomic structure would be based on the number of molecules, and the former number would be very, very large.

Answer 5

Because of the differences in saturation vapor pressure over ice versus water, tiny ice embryos grow at the expense of the tiny cloud droplets and eventually grow six evenly spaced branches. As more and more water vapor diffuses onto these branches, the ice crystal becomes increasingly heavy and begins to fall from the sky. As it descends, the ice crystal encounters very complex and variable atmospheric conditions, which ultimately contributes to its unique form.

Answer 6

God's amazing creativity.

Answer 7

- Cool question, don't know how God does it, But He does, so rad . . .

Answer 8

they're sh*t