Delicate needle-like growths of calcite or a related mineral, aragonite, are called frostwork. In places the frostwork may grow on top of cave popcorn or boxwork. The origin of frostwork is controversial. In Wind Cave, it seems to concentrate in passages with above average airflow where, it is thought, evaporation plays a role in its formation.

More Speleothems:
Boxwork | Calcite Rafts | Cave Popcorn |
Dogtooth Spar | Flowstone/Dripstone |
Gypsum Features | Helictite Bushes