Quote from above link:

"The sample chemistries the researchers found do not exist anywhere in nature. “Therefore,” says Barsoum, “it’s very improbable that the outer and inner casing stones that we examined were chiseled from a natural limestone block.”"

Barsoum et. al. (2006) based this conclusion apparently on a single source... Ireland (1947). It's cited 4 times in the paper in reference to what is asserted to be our present state of knowledge on limestone geochemisry/mineralogy with statements like "have not been reported on to date" (page 3793) and "we are unaware of any literature report" (page 3794). I asked Dr. Barsoum on his Blog [pyramids.blog.com] to provide a more up to date source for the claim and was given the old, pass-the-buck, stalling tactic of "If you think they are natural again the onus is on you to find the evidence", "I challenge you to come up with such a paper. I submit it does not exist and so whether i cite a 60 year old paper or a 2006 paper is totally irrelevant and immaterial." and "The geology of limestone has not really changed that radically in the last 40 years, has it?"! The 1947 paper was published before modern analytical techniques like XRF, XRD, EDS, TGA, etc etc etc. even existed... Also, Harrell & Penrod (1993) is not mentioned in Barsoum et. al. (2006) even thought it examined the same Lauer sample specimen they did in more geological detail and the results contradict some of Barsoum et. al. (2006) claims. For example, the Lauer sample contains only 3.3% SiO (and that includes some detrital quartz grains as well) and the sample is cemented together by calcite microspar and recrystallization. This is apparent from the Barsoum et. al. (2006) SEM microphotograph in fig. 3 with the distribution of grey coloured calcite grains and grain boundaries.

One might conclude from Barsoum et. al. (2006) that most of the specimens are weathered surface detritus, being described in one case as "most of the specimens were easily friable" in the caption of Fig. 2 for OC flakes (what they call "outer casing" i.e. the outer core masonry surface). The core masonry blocks of Fig 6b of the paper have been exposed to at most about 600 more years of direct atmospheric exposure than the more freshly exposed ones inside Vyse's hole in Fig 6a, and are asserted to be cast apparently based on the differences in appearance. Which of course has undergone chemical and mechanical weathered (i.e. altered from it original state, could be up to about 800 years of alteration due to direct exposure since the casing was removed, and add on to that a few thousand years of case hardening). This is not surprising since Davidovitus & Morris (1988) described one of their specimens from the Teti pyramid, tested by XRF in Davidovits (1984), as "weak and extremely weathered" yet it's compared to apparently unweathered GP and quarry samples.

Barsoum, M.W., Ganguly, A. & Hug, G.(2006) Microstructural Evidence of Reconstituted Limestone Blocks in the Great Pyramids of Egypt. J. Am. Ceram. Soc., 89, 3788–3796.

Davidovits, J. (1984) X-Ray analysis and X-Ray diffraction of casing stones from the pyramids of Egypt and the limestones of the associated quarries. Science in Egyptology. Manchester Universiy Press, p. 511-520.

Davidovitus, J & Morris, M. (1988) The pyramids an enigma solved. Hippocrene Books, New York, p. 263.

Harrell, J. A. & Penrod, B. E. (1993) The Great Pyramid Debate-Evidence form the Lauer Sample. Journal of geological education. 41, 358-363.

Ireland, H.A. (1947) Terminology for Insoluble Residues. Am.Assoc.Petrol.Geol. Bull., 31, 1479–90

Archae Solenhofen (solenhofen@hotmail.com)