Pyramids made of artificial stone?
Interesting story about geopolymers at Wired.com:
Professor Davidovits was awarded the French Ordre National du Mérite, and is President of the Geopolymer Institute. His most remarkable claim is that the pyramids were built using re-agglomerated stone, a sort of geopolymer limestone concrete, rather than blocks of natural stone. This would explain many of the mysteries of pyramid construction. Handling barrels of liquid concrete and casting in place would be much easier than moving giant blocks of stone. Remarkably, recent X-ray and microscopic study of samples has supported the theory that the pyramids are made of artificial stone.(h/t Lucianne.com)