The minerals of biology have two components, one of which is inorganic and the other organic. Understanding rests initially in the description of the factors that control the nucleation and growth of the inorganic components in the absence of organic materials, and in the study of the organic materials in the absence of the inorganic phase. Brief summaries of these studies are given and then an attempt is made to examine some of the interactive features of the whole mineral. There are very few generalizations that can be formulated yet since each mineral appears to be associated with the metabolic processes of a special cell. Partly, this is due to the diverse function that biominerals perform: supports, protection, sensors, storage and even homeostasis. We must also be aware of the vulnerable nature of precipitation control above the solubility limit. Many widespread medical problems involve the incorrect precipitation of iron and calcium compounds especially.