New mineral reaction path discovered

Transmission electron microscopic picture of the new reaction mechanism. The non-crystalline (amorphous) “transport” material emerges during the dissolution of the mineral on the right-hand side and occupies much of the pore space (bright) between the minerals. The newly forming mineral crystallizes directly from the amorphous substance (microscopic image: R. Wirth, GFZ).

With the aid of the latest, highly precise laboratory methods an international team of scientists with GFZ-participation identified a so far unknown reaction path for minerals in solid natural rocks. Classic examples of mineral reactions are the dissolution of a solid crystal in a liquid solvent - like a salt grain in a salad dressing - or the crystallization of a newly formed mineral from a solution - like the formation of carbonate crusts in water pipes. Mineral reactions in nature, like the formation and weathering of rocks, have large impacts on e.g. the formation of mineral resources, processes of the climate system, and natural hazards like earthquakes and volcanic eruptions.

The team of scientists from the University of Gothenburg, Sweden, the Keele University, UK, the GFZ, and the ETH Zürich, Switzerland, visualized traces of this formerly unknown process in a natural rock sample from California, USA. In their study published in Nature Communications the scientists describe the formation of larger mineral fragments that form a solid but non-crystalline phase. Supported by the FIB/TEM laboratory at GFZ led by Richard Wirth, equipped with transmission electron microscopy and nano-tomography, the team was able to detect interconnected pores within the rock sample with widths as small as a few nanometers – billionth’s of a meter. Within these pores the non-crystalline material must have been formed during the infiltration of water at a pressure of more than 10.000 times that of the atmosphere.

“Prefab construction” speeds up reactions

This newly discovered phase serves as an effective element transport medium during the reaction process. Franziska Wilke, head of the microprobe laboratory at GFZ section Inorganic and Isotope Geochemistry, and co-author of the study: “This is like building a house not from single bricks but from prefabricated components. This speeds up the process of building a house, just like the reaction process of the minerals in the newly discovered phase”.

The sampled rock has an exceptional history as it was buried in depths of more than 50 kilometers into the Earth’s interior during the subduction of the Pacific plate beneath the North American continent before being brought back to the Earth’s surface due to buoyancy and compression processes in the subsurface. Matthias Konrad-Schmolke, coordinating researcher of the project: “These rocks are perfect recorders of processes deep down in the Earth’s interior as mineral reactions are frozen in when these rocks return back to the surface”. It remains a matter of future research to see how common this newly identified reaction mechanism is in natural rocks and whether it only occurs deep in the Earth’s interior or also during rock transformation processes like earthquakes, volcanic eruptions, or resource formation. (ak)

Original study: Konrad-Schmolke, M., Halama, R., Wirth, R., Thomen, A., Klitscher, N., Morales, L., Schreiber, A., Wilke, F.D.H., 2018. Mineral dissolution and reprecipitation meditated by an amorphous phase. Nature communications 9:1637. DOI: