Blue Chalcedony identification

I have a necklace set with two blue stones that I always believed
was chalcedony. The blue was like the sky, and intense.

It has been in a bank vault for years and years, and the last time I
looked, one of the stones was turning white in areas and the other
seemed to have gotten a bit pale. The piece is German from the early
part of the 20th century, I think.

I may be wrong about the identification. I now wonder if it is some
other stone like a white onyx that was dyed blue. If so, what would
have made the dye wear off, sitting quietly in a bank vault?

If not, is there a blue stone that can fade in the dark, and looks
like blue chalcedony?

Hi: In my experience with blue calchadoney, it has done many things.
As a stone that refracts light from water spheres trapped in the
crystalline structure. This result in changes to the stone by
humidity changes, non-moisture environment, and have you ever seen
how paper desiccates things? Think of what a safety vault contains.
The only suggestion I have is to allow the stone to slowly
rehydrate, if you doe it to fast, the shock will fracture the stone.
I saw some nice blue at the gem show, here is a source for
calchdoney…TGI 1-800-656-gems… Another source is new era gems.