Why do snowflakes have 6 points? A Halifax expert breaks down the science of snow

·2 min read
All snowflakes have 6 points, although ice crystals can form into columns or needles under certain conditions. (CBC - image credit)
All snowflakes have 6 points, although ice crystals can form into columns or needles under certain conditions. (CBC - image credit)

The next time it snows, pay attention to those little flakes on your sleeve — they carry clues about what's happening above the clouds.

Mary Anne White is a professor emerita of chemistry at Dalhousie University, a member of the Order of Canada, and somewhat of an ice expert.

She's also on a quest to lead people away from inaccurate crafts.

"Snowflakes are usually six-fold symmetry, except places where you see them very badly cut out with, like, four-fold symmetry. It just drives me crazy," White said with a laugh.

"My granddaughter … wanted to know if I could help her on FaceTime to fold the paper to get the six points of the snowflake, so I was glad to do that."

CBC
CBC

Those six points happen because every snowflake is made up of billions and billions of water molecules, White said, and at the very core, are six water molecules essentially "holding hands" to make a hexagon shape.

The ways that huge numbers of water molecules can be added to that core hexagon are "so myriad," that there's no chance of having the same snowflake, she said.

All flakes start as water or condensation of some kind in the sky, and then the ice crystals form in different ways depending on temperature and humidity conditions.

Like a geologist examining a rock for information on an area's history, White said snow crystals can show what the atmosphere was like where it formed.

Thomas Clenche
Thomas Clenche

"If it's falling through space to a colder area, the ice molecules probably stick better. If it's falling through a more humid area, there are more water molecules to add to that," White said.

While the differences between snowflakes are certainly striking under a microscope, White said they're visible with a pocket magnifier or even the bare eye.

When the temperatures aren't too cold, hovering around 0 C, that likely means nice fluffy snowflakes, White said. Colder temperatures, from around –5 C to –10 C, bring long ice needles or columns. Colder still, around –15 C, flakes form again.

Ice in current research

Figuring out how and why ice forms in certain shapes is vital to White's own research.

Her team uses a method called "freeze-casting" to make ceramics that are porous, which can be used for various things like storing thermal energy or creating solar cells.

They mix ground-up ceramic with water, often including certain additives, which creates different shapes when frozen. White said they then freeze-dry the item and the ice melts, leaving behind empty spaces.

White said it's easy to forget how special snow is, especially after one has spent an hour shovelling the driveway.

"We see these beautiful crystals, they come to us for nothing out of the sky. We shouldn't curse them so much," White said.

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