For multi-phase samples such as basaltic wholerocks, 39 Ar K redistribution may be more of a problem than net 39 Ar K loss. You can always be sure you're reading unbiased, factual, and accurate information.
This ratio is For the J to be determined, a standard of known age must be irradiated with the samples of unknown age. Argon can mobilized into or out of a rock or mineral through alteration and thermal processes. Both techniques rely on the measurement of a daughter isotope 40 Ar and a parent isotope. Therefore, mafic rocks and minerals often contain less potassium than an equal amount of silicic rock or mineral. Such a phenomenon would great affect the shape of the age spectrum.