Author: Bernd Leiss

Abstract
Rock fabrics are quantitatively characterised by the microstructure and the texture. While the microstructure describes fabric parameters like the mineral phase composition, grain size, grain boundary configuration, shape anisotropy etc., the term texture refers to the sample-volume related crystallographic preferred orientations (CPO). In general, the quantitative characterisation of rock fabrics has two scopes: (1) the reconstruction of the rock forming history (e.g. deformation history) from the deduced rock forming mechanisms and processes (e.g. sedimentation, crystallisation, deformation, recrystallisation etc.) to understand e.g. mountain building processes and (2) the determination of the anisotropic physical properties (e.g. elasticity, thermal dilatation, magnetic properties, mechanical strength, etc.) to understand e.g. weathering processes of building stones, to interpret seismic data and to develop caverns for national gas reserves, final repositories for toxic waste, and fluid pathways for geothermal power plants, oil- and gas exploitation, CO2-sequestration.

Most rocks in the Earth’s crust and mantle are relatively coarse-grained and are composites of several mineral phases, usually of low crystal symmetry. In addition, geological structures are often heterogenous and show complicated structures due to polyphase deformation. Thus, volume-related texture analyses of rocks require (a) the measurement of large sample volumes, (b) high d-resolution in the diffraction patterns, and (c) the measurement of large sample series. Due to low absorption in matter, neutrons are especially suitable for diffraction experiments of large sample volumes.

In the following, some examples of currently running projects are given:
- the systematic structure-related analysis of sedimentary, deformed and recrystallised carbonate rocks revealed new texture types and now allows a differentiated interpretation of fabric developing mechanisms and gives new ideas on the deformation histories of colliding continents. From the strong anisotropic physical properties of single calcite crystals follow strong anisotropic physical properties of textured marbles. In combination with anisotropic grain shape fabrics, the different texture types influence the weathering processes of statues and the destroying bending of facade plates and tombstones.
- first quantitative neutron texture analyses of granites showed CPOs for the quartz and plagioclase phase. In addition to new ideas on the fabric development in granites, the results are important for predicting anisotropic crack development, for the safety of repositories, and for the initiation of fluid pathways for geothermal power plants etc.
- the texture analysis of rock salt from salt dome structures showed unexpected results and shall strongly contribute to the understanding of the mechanisms of salt diapirism and for the development of concepts of radioactive waste repositories in Germany.
- neutron texture analyses of the earth’s mantle derived material helps to understand the flow of the upper mantle and extremely fast exhumation processes.
- the comparison of texture-derived and experimentally measured anisotropic magnetic susceptibilites (AMS) on the basis of experimentally and naturally deformed synthetic carbonate-mica rocks contributes to improve the quantitative application of paleomagnetic analyses.