Process for quantifying the pyritic sulfur in a sedimentary rock sample, in which at least the following steps are applied: A. said sample is heated in an inert atmosphere, between a first temperature of between 100°C and 320°C and a second temperature of between 600°C and 700°C, while following a first temperature gradient of between 1°C/min and 30°C/min; B. at least one portion of the effluents resulting from said heating of said sample in an inert atmosphere is continuously oxidized, a first amount of SO 2 released as a function of time of said heating in an inert atmosphere is continuously measured, and at least one content of pyrolysis sulfur S pyrol and one content of pyrolysis pyritic sulfur S Pyrol Pyrit is determined from said first amount of SO 2; C. the residue of said sample resulting from said heating in an inert atmosphere is heated in an oxidizing atmosphere between a third temperature of between 280°C and 320°C and a fourth temperature of greater than or equal to 800°C, while following a second temperature gradient of between 1°C/min and 30°C/min; D. a second amount of SO 2 released as a function of time of said heating in an oxidizing atmosphere is continuously measured, at least one content of oxidation sulfur S oxy is determined from said second amount of SO 2, and at least one total sulfur content S Total is determined by the sum of said content of pyrolysis sulfur S pyrol and of said content of oxidation sulfur S oxy; characterized in that at least one content of pyritic sulfuric S pyrit contained in said sample is determined on the basis of a formula of the type: S Pyrit = p α β γ ⋅ S Pyrol Pyrit, wherein ρ ( α,β,γ) is a weighting function dependent on a parameter α representing a proportion of said pyrolysis pyritic sulfur relative to said total sulfur, on a parameter β representing an effect of the mineral matrix on said proportion, and on a parameter γ representing an effect of the organic matrix on said proportion, the values of said parameters being predetermined, said weighting function ρ(α,β,γ) being written in the form: p α β γ = 1 + β + γ α and in which: i) the parameter α is between 0.40 and 0.46, and is preferentially equal to 0.43, and ii) the parameter β is between: - 0.04 and 0.7, and is preferentially equal to 0.38 if said rock sample is of clay type, or - 0.7 and 0.9, and preferentially is equal to 0.78 if said rock sample is of marl type, or - between 0.85 and 0.97, and is preferentially equal to 0.9 if said rock sample is of limestone type, and iii) the parameter γ: - is equal to 0 if said rock sample contains organic matter of lacustrine and/or marine origin, or - is between 0.23 and 0.29, and preferentially is equal to 0.26 if said rock sample contains organic matter of terrestrial origin. A. said sample is heated in an inert atmosphere, between a first temperature of between 100°C and 320°C and a second temperature of between 600°C and 700°C, while following a first temperature gradient of between 1°C/min and 30°C/min; B. at least one portion of the effluents resulting from said heating of said sample in an inert atmosphere is continuously oxidized, a first amount of SO 2 released as a function of time of said heating in an inert atmosphere is continuously measured, and at least one content of pyrolysis sulfur S pyrol and one content of pyrolysis pyritic sulfur S Pyrol Pyrit is determined from said first amount of SO 2; C. the residue of said sample resulting from said heating in an inert atmosphere is heated in an oxidizing atmosphere between a third temperature of between 280°C and 320°C and a fourth temperature of greater than or equal to 800°C, while following a second temperature gradient of between 1°C/min and 30°C/min; D. a second amount of SO 2 released as a function of time of said heating in an oxidizing atmosphere is continuously measured, at least one content of oxidation sulfur S oxy is determined from said second amount of SO 2, and at least one total sulfur content S Total is determined by the sum of said content of pyrolysis sulfur S pyrol and of said content of oxidation sulfur S oxy; i) the parameter α is between 0.40 and 0.46, and is preferentially equal to 0.43, and ii) the parameter β is between: - 0.04 and 0.7, and is preferentially equal to 0.38 if said rock sample is of clay type, or - 0.7 and 0.9, and preferentially is equal to 0.78 if said rock sample is of marl type, or - between 0.85 and 0.97, and is preferentially equal to 0.9 if said rock sample is of limestone type, and - 0.04 and 0.7, and is preferentially equal to 0.38 if said rock sample is of clay type, or - 0.7 and 0.9, and preferentially is equal to 0.78 if said rock sample is of marl type, or - between 0.85 and 0.97, and is preferentially equal to 0.9 if said rock sample is of limestone type, and iii) the parameter γ: - is equal to 0 if said rock sample contains organic matter of lacustrine and/or marine origin, or - is between 0.23 and 0.29, and preferentially is equal to 0.26 if said rock sample contains organic matter of terrestrial origin. - is equal to 0 if said rock sample contains organic matter of lacustrine and/or marine origin, or - is between 0.23 and 0.29, and preferentially is equal to 0.26 if said rock sample contains organic matter of terrestrial origin.