Potassium dating accuracy
Geologists avoid dating glassy, polydeformed or very altered rocks with K-Ar, because these are known to sometimes be problematic .
A lot of the difficulties with the K-Ar method outlined by the other user here are addressed by the newer 40Ar/39Ar method which allows for: Therefore, the 40Ar/39Ar method yields results which are considered to be more robust.
Other methods, such as Isochron dating could potentially be used to show that the data are still consistent with current geological theory. I wrote the first draft thinking the entire range of reported dates represented the error bars on one sample, implying that the perceived dating error was not statistically significant. The study by Funkhouser and Naughton (1968) was on the xenoliths, not on the lava.
The xenoliths, which vary in composition and range in size from single mineral grains to rocks the size of basketballs, do indeed carry excess argon in large amounts.
I haven't heard of this being done, however if you have some evidence to this effect please share it. I have very little knowledge in the field of radioactive dating, and I'm not even sure if 1 is a true statement.
However if it is, then wouldnt this invalidate any results made using K-Ar dating?
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If you look at the data in Table 4 you will see that only a very very small portion of the 40Ar is radiogenic (Column 40Ar*) between 1.7 and 4 percent, relative to the total 40Ar.
Funkhouser and Naughton were quite careful to point out that the apparent "ages" they measured were not geologically meaningful.