On the occasion of the 14th edition of the Casablanca Heritage Days (12–18 May 2025), the exhibition “Lhajra Lkahla – Urban Geology of Casablanca’s Soils” offers an immersion into the material and geological history of a discreet yet essential element of the urban landscape: the dalle de mer, a black schist paving stone locally quarried and widely used between the 1920s and the 1970s. Proposed by studio lina jaïdi and Atelier BE., in collaboration with the École d’Architecture de Casablanca and Casa Mémoire, the exhibition questions the fate of this rock—formed over hundreds of millions of years, yet exploited for only a few decades. Far from a nostalgic return, it raises a central question: how can this vestige of functional modernity be reused today to imagine a city that is more sustainable and more attentive to its history and resources? Through a survey of existing conditions, rock fragments, cartographic surveys, a chronological timeline, oral history videos, and student prototypes, the exhibition explores the potential reactivation of this stone as a raw material for a new form of urban production—local, thoughtful, and rooted. Installed in the Timsit workshops, designed by Jean-François Zevaco in the 1950s and themselves paved with this black stone, the exhibition aligns with the national theme “Art Deco, between Heritage and Modernity,” extending this reflection through architecture, materials, and contemporary urban practices. “Lhajra Lkahla” is presented as a first step in a broader research project on urban geological resources and the possibilities of heritage reuse in Moroccan cities. It calls for the creation of new partnerships between architects, urban planners, geologists, institutions, and local authorities, so that these stones—now threatened with being discarded, crushed into rubble, or used as compacted aggregate—can become resources for the future.