Nanoscience will change the way we think about the world

Minerals, it is generally agreed, are naturally occurring crystalline substances having a characteristic and defined chemical composition. Each mineral expresses a set of specific physical and chemical properties. In addition, nanominerals have one critical difference. They express a range of physical and chemical properties depending on their size and shape.

“This difference changes our view of the diversity and complexity of minerals and how they influence Earth systems,” Hochella said.

A soil profile in the New Jersey Pine Barrens, where many nano-geo processes take place. Click here for more information.

Where nanominerals are

Nanominerals are widely distributed throughout the atmosphere, oceans, surface and ground waters, and soils, and in most living organisms, and even within proteins.

Oceans may be the principal reservoir, since they cover 70 percent of the Earth’s surface. There, nanominerals can come from processes associated with both living and non-living things, Hochella said. “Every mineral goes through a nanophase stage as it begins to grow. If they begin to grow at many sites, but don't continue to grow much after they form, you will end up with a lot of them and they may persist.”

In addition to growth and weathering, mineral nanoparticles can be generated from mechanical grinding. One of the most interesting and important places where this happens is along earthquake-generating faults in the Earth’s crust, reported by several researchers cited in the review.

There is a distinction between clusters of atoms and nanoparticles, Hochella said. “The difference seems to be that clusters start to approach the size of the smallest nanoparticles, but the atoms in many of these small clusters are not packed very tightly together. They are not dense. The nanoparticles represent a much denser packing of atoms, more like a real mineral, or at least approaching the atomic packing density of a larger mineral.”

The essence of nanoscience is observing, measuring, and understanding the variations of properties and reactivities as a function of size and shape. Structural variations that respond to size change or surface area change may include expansion and contraction of bonds, changes in bond angles, and variations in population and distribution of vacancies and other defects such as steps, kinks, edges, and corners. In the smallest nanoparticles, this results in a redistribution of electronic structure that affects reaction characteristics with the outside world. Measurement of these aspects remains a great challenge and priority for future mineralogists, the authors note.