While each and every snowflake can be generally said to be a hexagonal (six-sided) crystal, snowflakes come in many forms, from simple prisms and solid columns that look like rock crystals to the iconic and intricate flakes like stellar dendrites and simple stars. There are a variety of factors in play when it comes to the shape of each individual snowflake, including temperature, humidity and atmospheric pressure. A temperature difference of just a few degrees can mean the difference between one type of snowflake shape, such as a columnar needle, and another, such as a stellar plate.
A needle snowflake, which is long and slender like a needle, will form at temperatures around 23 degrees Fahrenheit, according to Caltech. The stellar plate, a flat, star-like flake, will form at temperatures near 28 degrees Fahrenheit. This means that a temperature difference of just 5 degrees can make a dramatic difference in a snowflake's shape.
In addition to temperature, the conditions in the atmosphere that the flake moves through as it forms will also influence its shape, but in more detailed ways than its overall form. The unique form of a snowflake's arm, for example, will be influenced by the conditions it experiences as it moves toward the ground.