Snowflakes come in many varieties, from the best-known star-shaped ‘stellar plates’, ‘sectored plates’ and ‘stellar dendrites’ - the latter of which you’ll most likely find hanging off a department store Christmas tree - to the less fancy ‘hollow column’ and ‘needle’ varieties, which look exactly like they sound. There are triangle shapes, rosettes, and pretty twelve-sided flower shapes too.
And then there are capped column snowflakes. These form into stubby column shapes before getting stretched out as they blow through the clouds. By the time they’re ready to fall, these snowflakes will have two plate-like, flower-shaped crystals attached on either end of a tiny ice column.
In the image above of a capped column snowflake viewed through an electron microscope at 50,000 times magnification, you can see what Jesus Diaz at SPLOID calls “slightly gross flabby little hair thingies” on both ends. This odd adornment is called rime ice.
Rime ice is the term used to describe a deposit of ice that forms on the wind-facing side of an exposed object, such as a tree, bush or telegraph pole. When supercooled cloud or fog droplets - which means they're still in an unfrozen state even at temperatures as low as -40 degrees Celsius - collide with an object, this causes them to freeze and crystallise almost immediately to form rime ice.
Rime ice forms on snowflakes under very specific atmospheric conditions, usually when snowflakes pass through supercooled cloud droplets. Contact between the two causes the cloud droplets to freeze or crystallise in unusual shapes on the snowflake. If a snowflake has rime ice crystals on it, it’s referred to as being ‘rimed’.