Carbon-rich dust is known to form in the circumstellar environmement of R Scl. The probing of such a process is crucial to understand the enrichment in heavy elements of the galactic interstellar medium. Using the spectro-interferometric measurements of the VLTI/MATISSE instrument, we managed to locate the seeds of dust formation around this bright AGB star. Indeed, the angular resolution of the ESO/VLTI in the spectral bands of MATISSE allows to scan its close stellar environment. Using the DUSTY code we give the main physico-chemical and geometrical key-parameters of the dust shell in agreement with the spectral distributions of both the ISO flux at high resolution in the mid-infrared and the MATISSE visibility in the LM and N bands. In order to better reproduce the 3.2µm features revealed in the object spectra, we used an analytical simple model resolving the radiative transfer equation that allows us to estimate the physical properties of the molecular layer.