It’s often said that no two snowflakes are the same shape.  Beginning as snow crystals which develop when microscopic supercooled cloud droplets freeze, complex shapes emerge as the flake moves through differing temperature and humidity regimes, such that individual snowflakes are nearly unique in structure.  Although statistically possible, it is very unlikely for any two snowflakes to appear exactly alike due to the many changes in temperature and humidity the crystal experiences during its fall to earth.