The Great Pyramid of Giza (Egypt) was built of four main varieties of rock--gray, hard, dense limestone; gray soft limestone; gray shaly limestone; and yellow limy shaly sandstone (in order of decreasing resistance to weathering). Since the facing was removed 1,000 years ago, products of weathering have formed talus slopes overflowing the blocks and banking against the base of the pyramid. An estimate of the rate of talus formation indicates that the pyramid annually loses only 0.01 percent of its total volume and could remain standing for 100,000 years.

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