『Abstract
　Building stones manufactured from contact metamorphic slates (Fruchtschiefer slate) from Teuma (Sachsen, Germany) were investigated for mineralogical alterations as well as for changes in porosity and surface roughness due to weathering. After weathering periods of several years to decades, the originally dark gray-colored slates show pale spots of several centimeters in size at the surface of building stones. The dark-colored and light-colored sections of the slate show no differences in mineralogy. Surface weathering did not result in newly precipitated minerals. It was also found that the observed differences in color are not caused by variations in sedimentary organic carbon concentration or in sulfide/sulfate concentrations. Obtained results instead indicate that dark surface sections may show a thin cover of recent organic matter (OM), e.g., living OM, soot, dirt,etc. Microscopic investigations suggested that this cover was exfoliated at light-colored surface sections. The observed disaggregation of the upper 2 mm of the building block material results in an increase in porosity. Porosity of black (unweathered) slate is ＜2 vol.％. Due to weathering, the slate's pores with diameters ＞1μm show a significant increase in frequency compared to the original pore size distribution. Porosity of weathered rock volumes increased to approx. 8 vol.％. Discolored surface sections show a higher surface roughness (root-mean-square roughness, Rq 〜 1μm） compared to dark-colored slate surfaces (Rq 〜 200 nm), both data are for cleavage planes. Preferentially, the discolored surface sections are located close to the edges of cut stones. This and the alteration in porosity, pore size, and surface roughness indicate that color changes of the slate are largely influenced by rock disaggregation proceeding from the edges into the center rather than by mineral dissolution/precipitation processes.

Keywords: Slate weathering; Theuma Fruchtschiefer (contact slate); Surface roughness; Rock disaggregation; Vertical scanning interferometry』

Introduction
Materials and methods
　Material
　Method
Results and discussion
　Petrography
　　Results
　　Discussion
　Mineralogy and geochemistry
　　Results
　　Discussion
　Porosity and surface roughness
　　Results
　　Discussion
Conclusions
Acknowledgments
Open access
References