These droplets attach themselves to nuclei of crystallization, which can be, for example, dust particles. This process begins only at temperatures below -12 degrees Celsius. The resulting ice crystals, which are less than 0.1 mm in size, sink downward increasing in size. As the size increases, the ice crystals take on different forms. The most common is the shape of six-pointed stars (at temperatures between -1 degrees Celsius and -3 degrees Celsius and between -10 degrees Celsius and -20 degrees Celsius), although there can be other shapes, such as lumps, needles, columns, plates (temperatures below -20 degrees Celsius). It depends on humidity, pressure, and air temperature.
