Abstract Size distribution and evolution of framboidal and euhedral microscopic crystals of pyrite (micropyrites, MPy) have been used for the last thirty years to deduce palaeo-redox conditions. The analysis of the MPy distributions can give valuable information about these palaeo-redox conditions. However, other information can also be retrieved from this type of analysis. In this work, we propose that the formation of new populations of MPy is a proxy of the transition from the anchizone to the epizone. High-resolution X-ray tomography (micro-CT) was used to determine the size distributions of MPy hosted in pelitic rocks subjected to different grades of low temperature metamorphism. These data were filtered and statistically analysed, which allowed us to find a statistical representative size distribution of the MPy present in the samples. The metamorphic grade was determined using the Kübler Index in combination with petrological and scanning electron microscopy (SEM) examination. The results show a relationship between metamorphic grade and MPy size distributions, and that new populations of MPy formed due to the effects of metamorphism. This new methodology for MPy size distribution has different potential applications in some fields of Earth sciences, such as palaeoenvironment reconstruction, ore mining or metamorphic petrology.

Abstract The Lede stone (Lutetian, Eocene) is an important historic building stone used in the NW of Belgium. In Ghent, it is dominant in the post-Romanesque built cultural heritage. Its use was restricted several times by socio-economic constraints. Since quarrying and production started to cease from the seventeenth century, periodic revivals favoured the use of Lede stone for new buildings and restoration projects. Sulphation is the main threat for the Lede stone as black crusts are the most common degradation phenomena on this arenaceous limestone. Around the turn of the nineteenth century, the Belgian Gobertange stone was the most widely used replacement material. Throughout the twentieth century, the use of replacement material shifted towards French limestones. However, their colour, texture and petrophysical properties differ from the Lede stone, for which a natural yellow–brown patina is very characteristic. In order to solve this mainly aesthetic issue, several new stone types are used as replacement stone in the twenty-first century, while many others have been suggested. It remains, however, difficult to find a replacement stone that matches the visual and petrophysical properties of the Lede stone. One remaining Lede stone quarry pit has increased its activity since 2011, offering the opportunity to use new Lede stone as replacement stone.