1.2.6: Biominerals

1.23 Clamshell

1.24 Teeth

1.25 Diatoms

Some living organisms produce crystalline materials through a process called biomineralization. The result may be shells or skeletal parts or simply the hardening of soft tissues. Mineralogists have identified more than 60 different biominerals created by animals, plants, fungi, and smaller organisms; three examples are shown below in Figures 1.23 through 1.25.

Biogenic processes produce other mineral equivalents too. For example, diatoms (like those seen in Figure 1.25), algae and sponges create structures made of various forms of silica – which is sometimes crystalline (and sometimes amorphous). And, bacteria deposit iron, copper and gold minerals, including iron oxides/hydroxides such as magnetite, goethite, and limonite. Some marine organisms produce aragonite, which is normally only stable under high pressures deep within Earth.Organisms that produce biominerals in shells, teeth, skeletons, or bones have existed for nearly 600 million years. Their hard parts are typically composed of organic equivalents of the minerals calcite (calcium carbonate – that makes up the shell shown) and apatite (calcium phosphate – that makes up the teeth shown).

The IMA definition says that a substance is not considered a mineral if it was formed entirely by an organic process. Sometimes, however it is difficult to make this distinction. In some limestones, for example, it is impossible to determine whether a mineral grain precipitated from water (inorganic) or is a biomineral (organic). And, today, some people consider biominerals to be the same as any other minerals. They note the many different kinds of crystalline biogenic substances that, in many cases, are nearly identical to naturally occurring minerals. Additionally, the IMA makes exceptions for some substances formed from organic material by geological processes, such as minerals that crystallize from organic matter in shales.