gypsum is =
HYDRATED CALCIUM SULFATE
IF IT DID NOT HAVE SULFUR IT WOULD NOT BE GYPSUM!
From what I understand they used a certain ash high in sulfates that when wet would decompose into sulfuric acid easily.
I’ve seen it personally how it rots copper in houses built with it.
“IF IT DID NOT HAVE SULFUR IT WOULD NOT BE GYPSUM!”
but it’s NOT supposed to be contaminated with free elemental sulfur, which was the big problem with the poisonous Chinese drywall.