Ice forms crystals that have hexagonal (six sided) symmetry. As ice crystals grow, they can only grow at specific angles. This is why snow flakes have six points. The angle between any two adjacent points is 60°. Now look at the end of one of the frost crystals in the photo. From the point, the crystal has five angles it can grow. It can grow straight ahead, 60° to the right, 120° to the right, 60° to the left, or 120° to the left. To grow, the crystal has to gain water molecules from the surrounding air. Because the crystal has already removed some of the water vapor from the air around it, the area straight ahead of the point usually has the highest concentration of water molecules. That means that the crystal will usually grow faster straight ahead than to either side. Each of the lines of frost is actually a single crystal.