Hoar Frost

Nikon D300 with 18-200mm VR Nikkor

Jasper National Park, Alberta, Canada

Hoar frost (also called radiation frost or hoarfrost or pruina) refers to the white ice crystals, loosely deposited on the ground or exposed objects, that form on cold clear nights --wikipedia

these feather-like frost formations were found at the mouth of the cave, where the warm/moist cave air meets frozen stone