Some Thoughts on the Definition of the Word Mineral

The term mineral has long been considered to apply only to inorganic substances, materials that exist independent of the biosphere. Coal, amber, copal and other hydrocarbons have not been considered to be minerals because of their organic origin. In some phosphate deposits, strengite and other phosphate minerals can be shown to have come from the action of bat guano on host rock. It has been suggested that in such cases, these deposits do not fit the strict definition of a mineral. It raises some interesting questions. It may indeed be of some benefit to consider just how many examples we might find of minerals that are not really minerals, and what their importance is to a proper understanding of natural history.

Many of the categories by which we catalog nature have undergone profound revision in recent decades. No longer is the biosphere divided neatly into plants and animals. Biologists recognize five kingdoms now, and there may even be more. The insights that followed from the work of Lynn Margulis and others has profoundly revised our understanding of living systems. The implications are there for the inorganic sciences as well. The family of minerals that participate in the chemistry of living systems includes all those secondary minerals that depend for their genesis on the action of oxygenated meteoric water on the primary minerals that are moved to the surface by volcanic activity. The reason is simply that biologists have shown in recent years that all of the atmospheric oxygen on earth came originally from bacterial photosynthetic processes over 2 billion years ago, and that the concentration of oxygen in our day and age is tightly coupled to biochemical systems presently living on the surface and in the air and oceans . It may be very instructive to reconsider just how interrelated these processes are, and just what we mean when we refer to an organic or to an inorganic material.

The transport of elements and minerals by biological systems has a great deal to do with the ecology of our planet. It has been demonstrated for example, that were it not for the action of certain biological systems, the composition of seawater would be much different. The sequestration of salts in evaporite deposits is due in large part to bacterial processes that stabilize barrier dunes and prevent them from being inundated. Without them, the oceans would be much more concentrated and the impact on life profound. For this reason evaporite minerals should be recognized as a special case of these quasi-organic materials.

Many of the boundaries we draw to name and differentiate the world we live in are arbitrary lines. We draw them to help us catalog and understand what we see, but they can also become blinders. They can be misleading if they’re not critically reexamined from time to time. The boundaries between organic and inorganic processes is probably one of those lines that is in need of revision, for the sake of the insights that always follow when we examine our preconceptions.

The mineralogy we love would be considerably less interesting were it not for the presence of life on earth. By implication, the presence or absence of mineral types on other planets can inform explorers about the status of life on those bodies long before any organisms are actually discovered.