Argon-Isotope Dating
A.
Isotopes of Potassium and Argon
The isotopes the KAr system relies on are Potassium (K) and Argon (Ar).
Potassium, an alkali
metal, the Earth s eighth most abundant element is common in many rocks and rock-forming
minerals....
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Argon-Isotope Dating
A.
Isotopes of Potassium and Argon
The isotopes the KAr system relies on are Potassium (K) and Argon (Ar).
Potassium, an alkali
metal, the Earth s eighth most abundant element is common in many rocks and rock-forming
minerals.
The quantity of potassium in a rock or mineral is variable proportional to the amount of
silica present.
Therefore, mafic rocks or minerals often contain less potassium than an equal
amount of silicic rock or mineral.
Potassium can be mobilized into or out of a rock or mineral
through alteration processes.
Due to the relatively heavy atomic weight of potassium,
insignificant fractionation of the different potassium isotopes occurs.
However, the 40
K isotope is
radioactive and therefore will be reduced in quantity over time.
But, for the purposes of the KAr
dating system, the relative abundance of 40
K is so small and its half-life is so long that its ratios
with the other Potassium isotopes are considered constant
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