Dehydration and clouding

The mirror of pyrite decay: a set of species that fail when the air is too dry, and they fail permanently.

Specimens that need the water

Hydrated minerals have water in the crystal structure. Remove it and the structure collapses.

The specimen goes chalky, loses transparency, cracks along cleavage and eventually crumbles. Unlike pyrite decay it is usually quiet: no smell, no acid, just a gradual loss of everything that made the specimen worth keeping.

What it looks like

Clear crystals going milky from the surface inward.

A fine network of cracks.

A powdery white surface that is the mineral itself, not a deposit on it.

And a specimen that was glassy in the dealer's case and is not in yours, which is how collectors usually first meet it.

The usual casualties

Laumontite, which is the textbook example and can dull within months in a dry room.

Chalcanthite and other soluble sulfates.

Borax and the borate group.

Some zeolites, variably.

The dealer often knows. Asking whether a species is sensitive before buying is normal and a good dealer will tell you, sometimes unprompted.

Keeping them

A sealed container holding its own humidity is the practical answer: the specimen equilibrates with a small volume of air rather than the room.

Some collectors keep a small damp buffer in with sensitive species, which works and needs watching so it does not become a mold problem.

Coating is a traditional treatment for laumontite in particular and it is a real intervention: it changes the specimen, it must be disclosed on sale, and it should be recorded on the label.

The cheapest defense is knowing which of your specimens are on this list, which is a catalog field rather than a memory.

References