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Some exotic examples from the snow crystal menagerie In addition to the normal snowflake forms see Guide to Snowflakes , there are also many unusual shapes that can be found floating from the sky. And, of course, you can find even more in our new book Not Your Ordinary Snow They're not real common, but you can spot them if you look.

Some snowfalls bring quite a few twelve-siders, although no one really knows what weather conditions are best for making them. Triangular Snowflakes You won't find any 4-, 5-, or 8-sided snowflakes in the wild, but you may spy some 3-sided crystals. Seeded by a speck of debris —dust, salt, a bacterium carried aloft—the tiny, delicate crystal grows and grows , with ever-more water depositing on to its surface as the flake is buffeted about within the cloud.

When the snowflake gets big and heavy enough it falls , changing its form as it encounters the steadily-warming temperatures near the surface. According to the Bytesize Science podcast of the American Chemical Society, these temperature shifts lend the snowflakes their intricate patterns:. What makes snowflakes white? Types of snowflake Whilst the variation of snowflake shapes is infinite, they can be broadly categorised into groups which give an indication as to what conditions the snowflake formed in.

Three of the broad types are: D endrite snowflake Perhaps the most eye-catching type of snowflake, the name means 'tree-like' recognising their branching structures. Thin plate Plates are essentially part-formed dendrites, the begin to form their intricate patterns but cannot obtain sufficient moisture to form the branches so form a less intricate flat plate. Sector plate Similar to a thin plate, a sector plate snowflake again lacks moisture but forms a hexagonal structure often with a star-like shape in the centre and the more visible attempts to branch.

You might also like. Freezing rain is a rare type of liquid precipitation that strikes a cold surface, and freezes almost instantly.

Read more. These axes define a three-dimensional coordinate system within the crystals' structure, and of course - as one would expect for describing three-dimensional bodies - there are 3 axes labeled a , b, and c.

For example, one can describe a crystal face as part of a plane that lies parallel to the a- and the b-axis and cuts the c-axis. This would work for quartz crystals as well, but for practical reasons and because of symmetry considerations, in quartz 4 axes defined in the hexagonal crystal system are used and labeled a 1 , a 2 , a 3 , and c Fig. Often there is no need to distinguish between a 1 , a 2 and a 3 and one simply refers to the a -axis or a 0 -axis.

Quartz crystals lack mirror symmetry. The mirror image of a quartz crystal is different from the original image, no matter where the mirror plane lies. Instead, quartz crystals show handedness : there are 2 types of crystals, left-handed and right-handed crystals. This is very similar to the human hand - you have a left and right hand.

Each of them is a mirror image of the other, but the mirror image of the left hand is not a left hand, so each hand itself lacks internal mirror symmetry unlike the human face, for example, which is roughly mirror symmetric. And this seems to be true of many real crystals, too. But this mirror symmetry is only an apparent one, the internal molecular structure of the quartz crystal cannot be mirrored: the atoms in a quartz crystal are arranged in parallel, corkscrew-like chains or helices.

A helix lacks mirror symmetry and is always either left- or right-handed a more thorough discussion of the handedness of quartz on a structural can be found in the chapter Structure.



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