(Formerly numbered Conservation of Archaeological and Ethnographic Materials 261.) Lecture, three hours. Introduction to igneous, sedimentary, and metamorphic rocks (geological context, mineralogical composition, macrostructure, and microstructure). Clay minerals: composition, structure, and properties. Rocks and stone: geographical distribution and occurrence, and usage by ancient cultures. Adobe: clay-based manmade materials. Mechanical and petrophysical properties of stone and adobe. Relationships between composition/structure and properties. Intrinsic and structural stability, resistance to weathering. Deterioration mechanisms and factors (physical, chemical, and biochemical). Letter grading.