Exactly what first attracted Phillips’ attention to the new science (Sander 1930) which became known as petrofabrics97 (Sander 1934) or structural petrology98 in the English-language literature is not known, but Phillips’ interest in this topic probably began during the course of his ‘Green Bed’ study. Petrofabrics is concerned with measuring the three-dimensional geographical orientation of mineral grains in rocks, primarily in order to deduce the directions of the tectonic forces responsible for making any preferred orientations detected.
It had long been appreciated, from field and laboratory studies on rocks (and also from metallurgical studies), that rocks deform under tectonic forces by recrystallization of existing minerals, chemical reactions producing new minerals, and by rotation of the mineral grains. In combination, these three processes construct in the rock a new texture or fabric, which reflects the tectonism that produced it. In order to determine the spatial orientation of this fabric correctly, it is therefore necessary to collect rock samples which are carefully orientated geographically. This is achieved in each case by making suitable marks on the surface of the rocks, defining the geographical and spatial orientation of each specimen, before it is removed from the outcrop.99 This enables the orientation in the field to be precisely transferred right through to the final thin-section of the rock.