1 Geography / Geology

 Carrières de la Préalle Sprimont S.A. quarries a blue stone called “ARDUIN – BELGIAN BLUE STONE ®,” marketed under the name “ARDUIN OF THE OURTHE.“ The La Préalle quarry is located in La Préalle, east of the former borough of Chanxhe (Sprimont), in the Ourthe-Amblève basin, in the central part of the northern flank of the Sprimont Syncline. Lambert coordinates: N 50° 30’ 10.285’’ E 5° 36’ 25.942’’.

The material is used as a building stone and masonry stone. It is a compact, non-porous, fossil-bearing limestone containing crinoids, gray in color when cut and dark gray when freshly fractured, with stylolitic joints parallel to the bedding. The mined layers form the Ecaussinnes Encrinite Formation (Tn3b), of Ivorian age, Tournaisian–Dinantian series, Lower Carboniferous.

Mining takes place in the open air; the benches have a strike of N88°E and a dip of 58°W in the western part of the pits, and a strike of N86°E and a dip of 50°W in the eastern part. The total mineable thickness in a single section is approximately 32.8 m.

The approval applies to those parts of the quarry that are of comparable quality, i.e., the homogeneous, massive production benches with low stylolite content within the operated area, clearly indicated on the cross-section (see Appendix 1, geological cross-section).

2 Petrography / Lithology

 Macroscopic description :

 “ARDUIN – BELGIAN BLUE STONE ®” is a compact limestone of sedimentary origin formed by the accumulation of countless crinoid remains cemented together into a microcrystalline calcite mass. Its gray color on a sawn surface and dark gray color on a fresh fracture surface are due to the organic carbon present between the calcite crystals. The stone develops a moderate gray patina typical of this material. This patina, which results from aging and is inherent to the rock’s composition, must be taken into account during restoration work.

In addition to crinoid remains, the limestone contains fragments of bryozoans (primarily Fenestella), brachiopod shells, and corals (either solitary or in colonies). A carbonated sedimentary rock is quarried in the quarry (2.2.1.2.b in PTV 819-4 Rock Classifications for Homologation, with reference to NBN EN 12670).

Microscopic description: 

“ARDUIN – BELGIAN BLUE STONE ®” is a bioclastic limestone dominated by crinoids; the other fragments consist of bryozoans, brachiopods, and corals. In some beds, pellets may be observed locally. It is a packstone, sometimes a grainstone (DUNHAM classification) or a biomicrite to a biospariet (FOLK classification, see NBN EN 12670). Other lithological features may be present (see TV 220).

Composition (for informational purposes): 

The average composition is 96 to 99 % carbonate (at least 80%, mainly calcite), 0 % to 1% quartz, 0.1% to 0.4 % iron (mainly sulfides: pyrite and marcasite) and 0.2 % to 0.4 % organic carbon.