Hoar is a type of frost that is characterized by a white coating of small ice crystals that form on objects outdoors when the temperature drops below freezing point. It is usually seen on surfaces such as plants, grass, roofs and even pavement. Hoar frost is usually most visible in late autumn and early winter, when temperatures are cold enough for ice to form on the exterior of objects. The frost has a white, shimmery and sparkly look, due to the way in which the ice crystals work together to refract light. The crystals can form in distinct patterns, which makes a hoar frost scene very visually beautiful.