K O Emery, Journal of Sedimentary Petrology, March 1960.
"At present, the pyramid is dry inside, even in the passage and chamber beneath the ground level. Measurements by Sutton (1945) show a humidity within the pyramid of only 47 to 61 percent, part of which is contributed by the perspiration of tourists. A 1mm to 3mm thick coating on the blocks was noted on the walls of the so-called Queen's Chamber: and in the horizontal passage leading to it. None was found elsewhere. This material consists of two to eight layers of salt of the following composition:
Sodium - 35.22%
Potassium - .02%
Calcium and magnesium - .40%
Chlorine - 54.14%
Sulfate - 1.01%
Water-insoluble - 9.21%
The water-soluble portion is thus about 99% halite, NaCl. Presumably, the salt was deposited during the few years that elapsed after the chamber was completed and before the pyramid was finished and faced. During this period the top was probably relatively flat (Lauer 1952) and able to collect rain water which could seep through the joints, dissolving some salts in the rock for later deposition in the open space of the chambers. The absence of the coating in the King's Chamber may result of the fact that the pyramid was finished so soon after this chamber was built that there was no time for leaching and deposition of salt, or that the salt was derived only from blocks that immediately line the chamber walls. In the King's Chamber these blocks are of granite not limestone."
And this is from Piazzi Smyth again, 'Life and Work at the Great Pyramid':
"Further it is particularly noteworthy, that in going North to South in the Horizontal Passage, saline incrustations are observable on walls and floor, beginning at about 150 to 200 distance (inches?) distance from the North end, and increasing in amount further South until at last both roof, walls, and floor are covered with a coating often near an inch thick, brown outside, white inside, and of almost stony hardness."
"This substance must be regarded as a modern exudation of the stone, for some letters scratched on the North Wall, with date 1824, have now a raised outline in the salty matter around and upon them." (Smyth would have seen this in about 1860).
"Similar incrustations, too, are to be seen on the Horizontal part of the entrance passage and walls of the sepulchral chamber of the Second pyramid. That the salt is almost entirely common salt, or chloride of sodium, Dr Wallace's recent analysis confirms. As well as by my own late finding that the recent cut and polished specimens of the Great Pyramid casing stones, after being put away for a few months in a closet are quite salt to the tongue.
But that does not explain off itself why there should be 12 times as much salt found in the construction of the stone forming the lining of the Queen's Chamber as in any other part of the Pyramid or Pyramid Hill yet examined."
Elsewhere Smyth describes an analysis of the salt which was, in his words, "identical to Common Salt."
Zahi Hawass also said that the Third Pyramid was closed for a period so that "salt could be cleaned off the walls". So there's salt in all three pyramids as Khafre's has some as well.