Any schoolchild knows that there cannot be two identical snowflakes. Each is unique. And a lot of factors impact its shape.
Their size vary from 0,2 mm wide up to 5 mm. Crystals which are smaller than "diamond dust" are too light to fall on the ground so they remain in the air, while larger crystals are too fragile and fall into pieces under the impact of the lightest breeze.
The final shape of the crystal will always have six branches.
The shape of a snowflake can tell us in what conditions it was froming.