1 Geography / Geology

 The Carrières de la Préalle Sprimont S.A. quarry a blue stone called "ARDUIN - BELGIAN BLUE HARDSTEEN ®", commercialized 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 north flank of the Synclinal of Sprimont. Lambert coordinates: N 50° 30' 10.285'' O 5° 36' 25.942''.

The material is used as a building stone and dressing stone. It is a compact, non-porous fossiliferous limestone, with crinoids, with a gray color when cut and a dark gray color when freshly fractured, with stylolitic joints parallel to the stratification. The mined strata form the Encrinite Formation of Ecaussinnes (Tn3b), age Ivorian, Tournaisian - Dinantian series, Lower Carboniferous.

Mining is done in open air; the banks have a stretch of N88°O and a slope of 58°Z in the western part of the quarries and a stretch of N86°O and a slope of 50°Z in the eastern part. The total mineable thickness in one piece is about 32.8 m.

The approval concerns the parts of the quarry of similar quality, i.e. the homogeneous, low stylolite massive production banks of the exploited whole, clearly marked on the coupe (see Appendix 1, geological coupe).

2 Petrography / Lithology

 Macroscopic description :

 "ARDUIN - BELGIAN BLUE HARDSTEEN ®" is a compact limestone of sedimentary origin resulting from the accumulation of innumerable remains of crinoids cemented together in a microcrystalline calcite mass. Its gray color when cut and dark gray color when freshly fractured is due to the organic carbon present between the calcite crystals. The stone acquires a medium gray patina typical of this material. This patina, which is due to aging and inherent in the composition of the rock, must be taken into account in restoration works.

In addition to remains of crinoids, the limestone contains fragments of bryozoa (mainly fenestella), shells of brachiopods and corals (standing alone or in colony). A carbonated sedimentary rock is quarried in the quarry (2.2.1.2.b in PTV 819-4 Classifications of rocks in the context of homologation with reference to NBN EN 12670).

Microscopic description: 

"ARDUIN - BELGIAN BLUE HARDSTEEN ®" is a bioclastic limestone with dominant crinoids; the other fragments are bryozoa, brachiopods and corals. Pellets may be observed locally in some banks. It is a packstone, sometimes a grainstone (DUNHAM classification) or a biomicrite to a biosparite (FOLK classification, see NBN EN 12670). Other lithological peculiarities may be present (see TV 220).

Composition (for information): 

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