Mineral inclusions in garnet: nanostructure-texture-genesis

Mineral inclusions embedded in larger host crystals can provide important information about the evolution of crystalline rocks or similar synthetic materials. Microstructural, crystallographic or compositional features like i) the inclusion distribution in the host crystal, ii) preferred shape orientation of inclusions, iii) the structure of the interface between inclusions and host crystal, iv) preferred crystallographic orientation of inclusion sets with respect to the host crystal and/or v) variations in the chemical composition of the involved minerals and their interfaces are used to infer the ambient conditions of inclusion formation. However, at present there are no unique criteria available that allow unequivocal determination of how inclusions formed.
Furthermore, the information available from characterization of mineral inclusion – host systems may differ when observing at different scales. By collaboration of researchers from the University of Vienna (Austria) and the Jožef Stefan Institute in Ljubljana (Slovenia) we intend to investigate mineral inclusions in garnet single crystals with various analytical methods that provide complementary information at different scales (millimeter, micrometer, nanometer and atomic scale). Different analytical instruments are required to cover this range of observation scales, and each method has certain strengths and weaknesses. Approaches working at millimeter to micrometer-scale can analyze sufficiently large sample domains to yield statistically representative information. On the other hand, time- and cost-intensive analyses at atomic scale resolution provide details of atomic arrangements of selected crystal domains, but only document very small sample portions that might not be representative. The combination of the different approaches therefore represents a promising way to analyze statistically representative features in sufficient detail.
We aim to identify the microstructural, crystallographic and compositional footprint of certain inclusion formation mechanisms like overgrowth, intergrowth or exsolution from the host crystal. Results are expected to provide tools for identifying the mechanisms and conditions of inclusion formation, which is of interest for geoscientists who aim at deciphering the past rock evolution, and material scientists who aim at designing material with defined properties. The results are expected to enhance understanding of the chemical and mechanical behavior of polycrystalline materials under changing ambient conditions.