
Snowflakes are luminous crystals of pure ice, clear and colorless. Water vapor freezes directly into ice crystals when clouds are very cold. Many crystals join together and float down as a snowflake. One snowflake can have over 100 crystals. Individual crystals falling on their own are too tiny to see. Snow looks sparkly and white because light reflects off all the surfaces of the ice crystals and blends together.
The air temperature determines the shape of a snowflake, each with its own unique design. Snowflakes have six sides (and sometimes 12) because water molecules line up in this repeating pattern when they freeze. They can form as stars, hollow columns, plates with flat sides or other types. Starting out as hexagons, they may sprout branches as they grow. Fernlike dendrites (or fernlike stellar dendrites) have narrow branches that look like tiny ferns. With their exceptionally large size and large thin plates, they are common and easy to spot. Fernlike dendrites are the largest snowflakes, some even measuring 0.4 inches (10mm). They form rapidly when the humidity is high and temperature is very low, about 5 degrees F (-15 degrees C).
Snowflakes are especially dazzling when you take a very close look. To see their beauty, catch them in the air or as they land. Walking across snow you hear the snap and pop as you break the crystals and trapped air escapes from inside.