The Quran's reference to "baked clay" in Quran 28:38 says:

This verse describes Pharaoh's request to bake clay for the construction of a structure, which is interpreted by some as a reference to the upper parts of the pyramids being made of baked clay—similar to modern concrete or cement.

For centuries, it was believed that the Egyptian pyramids, particularly the Great Pyramid of Giza, were built solely using cut limestone blocks. However, recent research by Professor Michel Barsoum and colleagues at Drexel University found that the blocks at the top of the pyramids were not natural limestone, but rather contained substances indicating they were likely baked and cast like modern concrete. Using electron microscopes, scientists discovered that the inner and outer casing stones of the pyramids contained a cementing phase with unusual characteristics: a high water content and an amorphous structure. This composition is not naturally found in limestone, suggesting that the blocks were artificially created using a form of early concrete. Additionally, some of the materials in these blocks showed the presence of silicon dioxide nanoscale spheres, further supporting the hypothesis that the pyramid's upper casing stones were made of a cement-like material rather than carved from natural limestone. This new understanding aligns with the Quranic mention of Pharaoh using baked clay for the construction of his monumental structure.

The Quran's reference to "baked clay" in the context of pyramid construction was once seen as an error, but modern scientific research supports this description. Electron microscope analyses have shown that parts of the Great Pyramids were made with a concrete-like substance, which could be seen as "baked clay" in the ancient context. Thus, the Quran's mention of such construction methods centuries before the discovery of this material composition evidences that the Quran contains knowledge beyond what was available in its time.