Snowflakes are made up of many small ice crystals that fall from clouds. Each individual ice crystal is no larger than the diameter of a human hair.
They're also called diamond dust because they sparkle in sunlight like sparkling dust. They're most common in bitter cold weather when air temperatures dip below 0 degrees Fahrenheit.
There are four main types of snowflakes: needles (small flakes), dendrites - mini Christmas tree-like structures -, plates, or columns. Each of these is shaped by the temperature at which they form in the air.
Needles are formed at temperatures between -8 and -10 Celsius. At even lower temperatures plates are formed, and at the very cold end of the spectrum -30 columns are produced.
They grow by accretion to other ice crystals in hexagonal formations. They can grow long arms and branching tendrils which create unique, artistic designs.
The Nakaya diagram of snowflakes, published in 1905, shows that their shapes depend largely on the combination of air temperature and moisture at which they are formed.
Each time the water vapor in a cloud changes, it changes how that vapor acts and how the molecules condense. That's why no two snowflakes are ever exactly the same.
Moreover, different conditions within the cloud and the order in which they occur change how the vapor acts and how the crystals form. This is what accounts for the differences between snowflakes - they are not identical, even under very close observation.
