ARE ALL SNOWFLAKES DIFFERENT?
There are not snowflakes that are exactly alike. A small snowflake contains about 10^18 water molecules, of these 10^15 will be water molecules that contain deuterium (heavy water). These are randomly spread throughout the snowflake, so the odds of two snowflakes being the same within the life of the universe is pretty much the same as zero. That does not even take into effect the dust center of the snowflake, or other contaminants that would be different due to the environment.