However, the Argon, a noble gas, constitutes approximately 0.1-5% of the Earth's present day atmosphere.
Because it is present within the atmosphere, every rock and mineral will have some quantity of Argon.
Ar total fusion measures ratios, making it ideal for samples known to be very argon retentive (eg. Total fusion is performed using a laser and results are commonly plotted on probability distribution diagrams or ideograms.
In order for an age to be calculated by the Ar technique, the J parameter must be known.
However, because each of these parameters is difficult to determine independantly, a mineral standard, or monitor, of known age is irradiated with the samples of unknown age.
The monitor flux can then be extrapolated to the samples, thereby determining their flux.
Step-heating is the most common way and involves either a furnace or a laser to uniformily heat the sample to evolve argon.
Therefore, mafic rocks and minerals often contain less potassium than an equal amount of silicic rock or mineral.
Argon loss occurs when radiogenic K by a fast neutron reaction) can be used as a proxy for potassium.
Therefore, unlike the conventional K/Ar technique, absolute abundances need not be measured.
The method most commonly used to date the primary standard is the conventional K/Ar technique.
The primary standard must be a mineral that is homogeneous, abundant and easily dated by the K/Ar and Ar methods.