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Nano-scale investigations of mineral reaction mechanisms

Research project

Short description

Reactions among solid materials, such as minerals, are of utmost importance for society. Apart from many crystalline materials we use every day, minerals are used in large variety of industrial processes. Furthermore, mineral reactions in the solid Earth are also of societal concern e.g. volcanic eruptions. Despite this fundamental importance mineral reaction mechanisms, i.e. the process during which minerals are formed and transformed, is only partly understood. The reason for that is that mineral reactions occur at nano- and atomic-scales, which needs most modern high-resolution analytical instruments to investigate them. In this project we collaborate with different laboratories in Sweden and other countries to study and quantify the mechanisms by which minerals react with each other as well as with fluids, such as water and CO2.

Why mineral reactions matter

You might believe that chemical reactions between minerals are important for only a few people like mineral collectors or geologists. In fact, mineral reactions, which involve destruction and/or creation of a framework of atoms, play a fundamental role in everybody’s life. The production of many functional materials, such as computer chips, catalysts, ceramics and mechanical tools involve at some stage the formation or decomposition of a new mineral. Mineral reactions in nature include the weathering of rocks and the formation of solid rock from molten lava flows. These reactions influence the climate, produce ore deposits and play important roles in natural hazards, such as earthquakes and volcanic eruptions.

Natural mineral reactions occur at a large range of different rates, as they often involve an atom-by-atom dissolution of the solid crystal in a liquid solvent, like a salt cube in your salad dressing, and an atom-by-atom crystallization of the newly formed mineral from the solution, like the formation of carbonate crusts in your water pipes. Mineral solution and re-formation in these classical examples can be seen as the rebuilding of a new Lego® house from single bricks that have been taken from a previous building.

Laboratory experiments, however, have shown that some naturally occurring mineral reactions might indeed proceed much faster than predicted by this ¨classical¨ view on the reaction process. Nature has obviously found a way of surrounding the slow and tedious destruction, transport and re-formation process during mineral reactions.

We could now demonstrate that mineral reactions in solid natural rocks can follow a different reaction path. We observed, instead of the atom-by-atom dissolution of the reacting mineral, the formation of larger mineral fragments that form a solid but amorphous, i.e. non-crystalline, phase that serves as a very effective element transport medium during the reaction process. The formation of a new mineral from this amorphous substance seems also facilitated by the non-crystalline precursor. This new process is as if you would take apart your Lego® house not entirely in order to build a new one, but rather use larger parts of the old one to fit them into the new building. It is obvious that such a process enables much faster element (brick) transfer and much higher reaction (rebuilding) rates.

Utilizing a new mass spectrometer with a nanometer-scale resolution at Gothenburg University together with transmission electron microscopy and nano-tomography at the GFZ in Potsdam the we detected interconnected pores with widths as small as a few nanometers (one billionth of a meter) within which the amorphous material was formed during the infiltration of water at a pressure of more than 10.000 times that of the atmosphere.

Now the question arises how common this reaction mechanism is in natural rocks and inasmuch higher reactions rates during rock transformation influence large scale processes, such as earthquakes and ore formation.

Transmission electron microscope image of an ongoing mineral reaction. Calcium-amphibole (Amph1), a common mineral in the Earth’s crust, is reacting to form a chemically different variety (Sodium-Amphibole).
Photo: Matthias Konrad-Schmolke
Water is the main element transport medium during mineral reactions. This image shows a mapping of the water content in a mineral taken with a special mass spectrometer at Gothenburg University.&nbsp;<br /> Foto: Matthias Konrad-Schmolke
Photo: Matthias Konrad-Schmolke