Potassium 40 argon 40 dating
The target mineral is separated using heavy liquids, then hand-picked under the microscope for the purest possible sample.
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.
Rock samples are recorded, marked, sealed and kept free of contamination and excessive heat on the way to the lab.
But micas, plagioclase, hornblende, clays and other minerals can yield good data, as can whole-rock analyses.
The rock sample to be dated must be chosen very carefully.
Any alteration or fracturing means that the potassium or the argon or both have been disturbed.
Another concern with K-Ar dating is that it relies on there being no Ar in the rock when it was originally formed, or added to it between its formation and our application of the K-Ar method.
Because argon is inert, it cannot be chemically incorporated in the minerals when they are formed, but it can be physically trapped in the rocks either during or after formation. If the source of this argon is atmospheric contamination, then we can correct for this.Potassium occurs in two stable isotopes (Ar atoms trapped inside minerals.