Mirabilite — sodium sulfate — forms in the most extremely dry parts of the cave.

It appears as delicate crystalline flowers and needles, different in texture and chemistry from gypsum but equally the product of slow evaporative deposition.

Epsomite — magnesium sulfate — appears in similar conditions.

There are other sulfate minerals too: hexahydrite, blodite, celestine.

Mammoth Cave has been called the most complex cave sulfate mineralogy in the world, a distinction that reflects the specific combination of geological conditions — the limestone, the cap rock, the ancient water chemistry, the dry air — that no other known cave system replicates in exactly the same way.

These minerals are fragile.