Using ecological materials such as raw earth represents an ancestral building practice that has been revisited for modern construction, thanks to its availability, low cost, environmental friendliness, and thermal properties, which offer optimal insulation and thermal comfort. This article explores the development of a new composite based on raw earth reinforced with 15% mussel shells, a by-product of the aquaculture industry, combined with two stabilizers: lime or cement (3%, 5% and 8%), in distinct formulations. This study aims to characterize the chemical and mineralogical composition of the soil and mussel shells and the thermal and mechanical properties of the composites. The results indicate that the gradual addition of lime to the soil-mussel shell mixture decreases dry density, which reduces dry mechanical strength due to increased porosity but enhances thermal properties. Conversely, incorporating cement into the soil-mussel shell mixture improves significantly mechanical properties while limiting the thermal performances.