Installation for determining the age of a sample of a mineral of a rock, the installation comprising: - a device for analysing a sample of a mineral of the rock comprising a number ( 40 Ar measured) of argon-40 atoms and a proportion by mass ( 40 K) of potassium-40 in the sample, the analysis device comprising - means for treating the rock which are to extract a sample of a mineral of the rock and free the argon-40 and the natural potassium, which comprises potassium-40, from the sample; - first analysis means which are to determine the number ( 40 Ar measured) of argon-40 atoms in the sample; and - second analysis means (12, 29) which are to determine the proportion by mass ( 40 K) of potassium-40 in the sample; characterised in that - the means for treating the rock comprise a laser which is to be fired at the rock in order to ablate the sample of the rock and form a plasma from the sample; - the first analysis means are capable of analysing the gases obtained from the plasma in order to determine the number ( 40 Ar measured) of argon-40 atoms in the sample; - the second analysis means (12, 29) are capable of analysing the plasma formed by the laser in order to determine the proportion by mass ( 40 K) of potassium-40 in the sample; and characterised in that the installation further comprises - means (9, 12) which are to establish a database from at least one reference rock of known age (t*), the database associating the mass (m*) of a reference sample of a mineral of the reference rock with the characteristics (D*, I*) of fire of the laser and with the nature (N*) of the mineral constituting the reference sample; - means which are to determine, with the aid of the database so established, the mass (m) of the sample from the characteristics (D, I) of the laser fire effected in order to ablate the sample and from the nature of the mineral constituting the sample; and - means which are to calculate the age (t) of the rock from the mass (m) of the sample, from the number ( 40 Ar measured) of argon-40 atoms and from the proportion by mass ( 40 K) of potassium-40 in the sample. - a device for analysing a sample of a mineral of the rock comprising a number ( 40 Ar measured) of argon-40 atoms and a proportion by mass ( 40 K) of potassium-40 in the sample, the analysis device comprising - means for treating the rock which are to extract a sample of a mineral of the rock and free the argon-40 and the natural potassium, which comprises potassium-40, from the sample; - first analysis means which are to determine the number ( 40 Ar measured) of argon-40 atoms in the sample; and - second analysis means (12, 29) which are to determine the proportion by mass ( 40 K) of potassium-40 in the sample; characterised in that - the means for treating the rock comprise a laser which is to be fired at the rock in order to ablate the sample of the rock and form a plasma from the sample; - the first analysis means are capable of analysing the gases obtained from the plasma in order to determine the number ( 40 Ar measured) of argon-40 atoms in the sample; - the second analysis means (12, 29) are capable of analysing the plasma formed by the laser in order to determine the proportion by mass ( 40 K) of potassium-40 in the sample; and characterised in that the installation further comprises - means (9, 12) which are to establish a database from at least one reference rock of known age (t*), the database associating the mass (m*) of a reference sample of a mineral of the reference rock with the characteristics (D*, I*) of fire of the laser and with the nature (N*) of the mineral constituting the reference sample; - means which are to determine, with the aid of the database so established, the mass (m) of the sample from the characteristics (D, I) of the laser fire effected in order to ablate the sample and from the nature of the mineral constituting the sample; and - means which are to calculate the age (t) of the rock from the mass (m) of the sample, from the number ( 40 Ar measured) of argon-40 atoms and from the proportion by mass ( 40 K) of potassium-40 in the sample.