5:15 PM - 6:45 PM
[MIS02-P03] Characterization and Petrophysical Analysis of the "Pierre de Langres" Limestone for Heritage Conservation
Keywords:Pierre de Langres, limestone, clay content, petrophysics
The city of Langres is renowned for its distinctly "mineral" appearance, owing to its primary monuments and dwellings crafted from dressed stone facades. The city's identity is closely intertwined with its stone, the "Pierre de Langres," which highlights a direct relationship between the layers of the plateau or promontory and the constructed buildings. The "Pierre de Langres" is a well-known construction material, historically mined from the “Fontaine au Bassin” quarry in Saint-Ciergues, sourced from the Bajocian layers (Middle Jurassic). It is a limestone packed with stems and an argillaceous matrix, known as "Calcaire à Entroques" (Crinoidal limestone). The appearance is a reddish-brown stone, with variable color intensity depending on the clay proportion.
This study aims to characterize petrographically and petrophysically the "Pierre de Langres" based on the various sub-facies of this limestone. Four distinct varieties of the “Pierre de Langres” have been identified based on its clay/crinoids fragments ratio, which are in relation to their quality as ornamental stone:
- Homogeneous variety with contiguous and scarce matrix
- Variety with non-contiguous stems in an abundant orange matrix
- Variety with pentacrinite ossicles (fairy money) and sea urchin spines, exhibiting variable clay content. According to stonecutters, the presence of pentacrinite ossicles indicates quality and suitability for use as slabs and thresholds.
- Bioturbated and heterogeneous variety
These four variations were characterized from a petrophysical standpoint. Initially, image analysis quantified the matrix/grain ratio. Water porosity tests were conducted to ascertain differences in this property. Capillarity and sound velocity tests were performed in three directions to establish anisotropy and transfer properties, as well as relationships with porosity.
Significant differences were observed among the varieties of Pierre de Langres, enabling a deeper understanding of its deterioration mechanisms and optimization for restoration purposes.
This study aims to characterize petrographically and petrophysically the "Pierre de Langres" based on the various sub-facies of this limestone. Four distinct varieties of the “Pierre de Langres” have been identified based on its clay/crinoids fragments ratio, which are in relation to their quality as ornamental stone:
- Homogeneous variety with contiguous and scarce matrix
- Variety with non-contiguous stems in an abundant orange matrix
- Variety with pentacrinite ossicles (fairy money) and sea urchin spines, exhibiting variable clay content. According to stonecutters, the presence of pentacrinite ossicles indicates quality and suitability for use as slabs and thresholds.
- Bioturbated and heterogeneous variety
These four variations were characterized from a petrophysical standpoint. Initially, image analysis quantified the matrix/grain ratio. Water porosity tests were conducted to ascertain differences in this property. Capillarity and sound velocity tests were performed in three directions to establish anisotropy and transfer properties, as well as relationships with porosity.
Significant differences were observed among the varieties of Pierre de Langres, enabling a deeper understanding of its deterioration mechanisms and optimization for restoration purposes.