Professor Bejan explain in this article from Mechanical Engineering, why every snowflake is not unique about its principle, the constructal law.

Every snowflake conforms to only one architecture: a flat star with six fishbones connected at the center.

What’s more, that structure is predictable provided that we recognize the underlying principle: first, that something flows, in this case heat, and, second, that the natural tendency of all flows is to evolve
into architectures that provide easier access.

It’s another example of the constructal law.

• Adrian Bejan, Every snowflake is NOT unique, Mechanical Engineering, January 2015, pp.40-41.
• Why Every Snowflake is NOT Unique, Duke University Professor Adrian Bejan, YouTube Video.
• Pauline Gravel, L’architecture des flocons de neige, LeDevoir.com