blue ice
Noun
Meaning
Ice that is blue in colour, formed by compressed snow on a glacier having its air bubbles squeezed out.
(aviation) Human waste that has leaked from an aircraft, frozen at high altitude, and fallen to earth.
Source: en.wiktionary.orgExamples
The road was frozen. The village lay quiet under the cold sky. Komako hitched up the skirt of her kimono and tucked it into her obi. The moon shone like a blade frozen in blue ice.
Blue ice is usually hard.