Metastability in Nature: Amorphous Mineral Precursors and Crystallization in One Dimension

Seminar | October 25 | 4-5 p.m. | 348 Hearst Memorial Mining Building

 Dr. Michael Whittaker, Postdoc, Energy Geosciences Division, Lawrence Berkeley National Lab

 Materials Science and Engineering (MSE)

There are over 5,000 mineral species on earth, many of which are metastable. All of the predicted >1,500 minerals that are likely to exist but have yet to be discovered,(1) also reside above the energetic ground state. Organisms have contributed significantly to the metastability of earth's mineralogy by creating far-from-equilibrium conditions in which new minerals form. Recent research in our lab has shown that a significant portion of the tree of life, much of which was likely responsible for driving earth' past geological evolution, were previously unknown because (a) they are difficult to culture and (b) are obligate symbionts of other organisms.(2) Not only have organisms shaped earth's geological diversity, many have co-opted naturally available minerals to form bones,
teeth and shells. Across almost all biomineralizing organisms, the use of metastable mineral precursors to crystalline biominerals allows for the ambient temperature synthesis of otherwise refractory materials like carbonates, phosphates, oxides, and sulfides. This paradigm is not limited to biology. I will show how the amorphous
precursor strategy can be used to synthesize a metastable, high-temperature (>525 C) carbonate phase in vitro with a far-from-equilibrium composition that has mechanical properties surpassing biomineral analogs.(3) I will also show new results on the
crystallization of montmorillonite, a natural layered material comprising 1 nm thick crystalline sheets separated by molecular layers of water. Initially random stacking can be induced to crystallize along the stacking direction via the concerted rotation of
individual layers, demonstrating that the amorphous -> crystalline transition can manifest in myriad ways. As humans continue to inject energy into both mineral and material systems, controlling transformation pathways between metastable phases will
vastly expand the number of structures (and therefore properties) available to us, well beyond the 100,000 known inorganic crystalline phases, over half of which are metastable. (4)

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