" I was hoping to be able to get into the Queen's Chamber while I was in Egypt in 1986 to get a sample of the salt for analysis. I had speculated that the salt on the walls of the chamber was an unwanted, though significant, residual substance caused by a chemical reaction where hot hydrogen reacted with the limestone. Unfortunately, I was unable to get into the chamber because a French team was already inside the Horizontal Passage, boring holes into what they hoped were additional chambers. (It was discovered, after I left Egypt, that the spaces contained only sand.)
As it turned out, my research would have been redundant. Noone reported in his book that another individual had already had the same idea and done the work. In 1978, Dr. Patrick Flanagan asked the Arizona Bureau of Geology and Mineral Technology to analyze a sample of this salt. They found it to be a mixture of calcium carbonate (limestone), sodium chloride (halite or salt), and calcium sulfate (gypsum, also known as plaster of paris). These are precisely the minerals that would be produced by the reaction of hot, hydrogen-bearing gas with the limestone walls and ceiling of the Queen's Chamber.
[...]
The interior chambers of the Great Pyramid have the appearance of being subjected to extreme temperatures; and [...] the broken corner on the granite box shows signs of being melted, rather than simply being chipped away. "

― Christopher Dunn , The Giza Power Plant: Technologies of Ancient Egypt