The selected size fraction is cleaned in ultrasound and acid baths, then gently oven-dried.
The target mineral is separated using heavy liquids, then hand-picked under the microscope for the purest possible sample.
Also, the cheaper K-Ar method can be used for screening or reconnaissance purposes, saving Ar-Ar for the most demanding or interesting problems.
These dating methods have been under constant improvement for more than 50 years.
This mineral sample is then baked gently overnight in a vacuum furnace.
Young rocks have low levels of Ar, so as much as several kilograms may be needed.Then the gas sample is cleaned of all unwanted gasses such as H, nitrogen and so on until all that remains are the inert gasses, argon among them.Finally, the argon atoms are counted in a mass spectrometer, a machine with its own complexities.Three argon isotopes are measured: Ar is determined by comparison to it.Variations in this data may point to errors anywhere in the process, which is why all the steps of preparation are recorded in detail.