Fabrics and structure of metamorphic flagstones and implications for industrial quality

Abstract

Metamorphic flagstones are characterised by a regularly spaced mica foliation separated by quartzo-feldspathic domains, along which the rocks can be cleaved into commercial slabs. In the thrust nappes of the Scandinavian Caledonides, such deposits are essentially developed from psammitic rocks in high-strain zones. Recent investigations have shown that the industrial quality of many flagstone deposits can be linked to several aspect of the tectonometamorphic development of the rocks, and especially to rapid vertical and lateral variations in strain. Field relations and microtextures from three different flagstone deposits are described and used as examples. Finally, a structural and textural characterisation of flagstones is proposed.