Guide to Snowflakes
... A look at the different types of falling snow ... |
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Although no two
snowflakes are exactly alike, their forms usually fall into several
broad categories. Check out the basics below, and then impress your
friends with your knowledge of the diverse snowflake group.
These pictures
are from the Rasmussen & Libbrecht collection. (To see more snowflakes
click here) |
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The Basic Snowflake Forms |
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  Stellar
Dendrites
Dendrite means "tree-like", which describes the multi-branched
appearance of these snow crystals. Stellar dendrites have six
symmetrical main branches and many randomly placed sidebranches.
These crystals are sometimes
5mm or more in diameter, yet they are quite flat and perhaps less than
0.1mm thick. |
  Sectored
Plates
Numerous ice ridges seem to divide the plate-like arms of these snow
crystals into sectors -- hence
they are called sectored plates. Like the stellar dendrites,
sectored plates are flat, thin slivers of ice that fall to earth in a
stunning diversity of complex shapes.
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  Hollow
Columns
Plate-like snow crystals may get more attention, but column-shaped
crystals are the main ingredients of many snowfalls. These hollow
columns are hexagonal, like a wooden pencil, with conical hollow
features in their ends. |
Needles 
Columnar crystals can grow so long and thin that they look like
needles. Sometimes these ice needles contain thin hollow regions, and
sometimes the ends split into additional needle branches. |
  Spatial
Dendrites
Not all snowflakes form as thin flat plates or slender columns. Spatial
dendrites are made from many individual ice crystals jumbled together.
Each branch is like one arm of a stellar crystal, but the different
branches are oriented randomly. |
  Capped
Columns
These crystals started out growing as columns, but then suddenly
switched to plate-like growth. This happens when a crystal is blown
into a region with a different temperature. |
  Rimed
Crystals
Snowflakes grow up in clouds, and clouds are made of small water
droplets. Droplets that freeze onto a falling snow crystal are called
rime, and these pictures show crystals that picked up different
amounts of rime. Sometimes a snowflake becomes just a ball of rime,
which is then called graupel, or soft hail. |
 Irregular
Crystals
Snowflakes can have a hard life blowing about in a turbulent cloud, so
that many arrive on the ground broken, ill-formed, and generally in bad
shape. Warm snowfalls tend to bring the most irregular snowflakes,
especially when the wind is blowing hard. |
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The categories above are just the basic snowflake types. You can see
some of the more exotic specimens at
Unusual Forms. |
| A bit of
terminology: What we usually call snowflakes are more accurately called
snow crystals, which are single crystals of
ice that often show six-fold symmetry. A snowflake is
a more general term that can mean an individual snow crystal, a
polycrystalline form like a spatial dendrite, or a cluster of many snow
crystals stuck together. One often sees snowflakes that look like
puff-balls, sometimes made of thousands of individual snow crystals,
falling from the sky. |
| Taken
from
http://www.its.caltech.edu/~atomic/snowcrystals/class/class.htm. |
