These interesting looking specimens are commonly known as "cave calcite" or "cave popcorn". Actually, geologically speaking, these are NOT calcite, but instead aragonite. Aragonite and calcite are chemically the same (calcium carbonate), but form crystals differently.
This mineral forms within caves, mines and moist areas that are rich in limestone. Formations occur as stalactites and stalagmites. Cave calcite forms in a variety of colors ranging from clear, to milky white, and, as seen in this listing as a rusty oranges. These colors, in addition to their coral-like formations, make cave calcite great addition to any collection.
Note: Though cave calcite, as the name implies, are found in caves, these specimens have been harvested as a result of a mining operation that would have destroyed these pieces for all time. No caves were harmed for the specific purpose of collecting these specimens.