This chapter explores why groups of minerals frequently coexist. A chemical equilibrium of pressure, temperature, and composition defines the conditions under which rocks form and determines which minerals are present. Quantitative understanding of mineral associations became possible in the 20th century when it became feasible to approximate geological conditions in the laboratory. Phase diagrams are used to determine which minerals form under which conditions.
Topics covered in Chapter 20 include: Introduction to Chemical Equilibrium Binary Phase Diagrams Ternary Phase Diagrams Mineral Associations A Quick Journey to the Center of the Earth The Rock Cycle, Mineralogy-Style