Selenite, satin spar, desert rose, and gypsum flower are four varieties of the mineral gypsum; all four varieties show obvious crystalline structure. The four "crystalline" varieties of gypsum are sometimes grouped together and called selenite

The huge mines at Naica have been excavated for years, but in 1975 a massive area was drained so mining operations could take place. It was more than 25 years before two miners stumbled across the vast Crystal Caves and the incredible collection of gypsum was discovered.

https://www.telegraph.co.uk/travel/picturegalleries/8660364/Amazing-caves-of-giant-crystals-inside-the-Naica-Mine-in-Chihuahua-Mexico.html?image=2