You also have potassium-- and once again writing the K and the 19 are a little bit redundant-- you also have potassium There's another layer of volcanic rock right over there. For useful info on corrections to some misconceptions regarding radiometric dating try: In rubidium-strontium dating, micas exclude strontium when they form but accept much rubidium. By determining the number of tracks present on a polished surface of a grain and the amount of uranium present in the grain, it is possible to calculate how long it took to produce the number of tracks preserved. But it hopefully makes the point that Ar-Ar dating can take data from small samples based on mass spectrometry.
When the rock recrystallizes it becomes impermeable to gasses again.
Potassium-argon (K-Ar) dating
Now, some of the other isotopes of potassium. How are Samples Processed? Unfortunately, our editorial approach may not be able to accommodate all contributions. These each have 19 protons and 21 neutrons in their nucleus. The energy-level diagram below is based on data accumulated by McDougall and Harrison.