A branch of geology that uses microscopic examination of thin sections to describe and systematically classify rocks, petrography is used throughout construction projects from defining the quality of materials before construction to revealing the causes of concrete deterioration long after construction is complete. Petrographic equipment and techniques have been adapted to characterize concrete. But there are some questions that even the best petrographer cannot answer, such as whether a chemical admixture was used in the mix and, if so, how much, what type of portland cement was used, or what the water/cement ratio was.