The quantity of potassium in a rock or mineral is variable proportional to the amount of silica present.Therefore, mafic rocks and minerals often contain less potassium than an equal amount of silicic rock or mineral.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.For the J to be determined, a standard of known age must be irradiated with the samples of unknown age.Because this (primary) standard ultimately cannot be determined by Ar, it must be first determined by another isotopic dating method.Traditionally, this primary standard has been a hornblende from the Mc Clure Mountains, Colorado (a.k.a. Once an accurate and precise age is determined for the primary standard, other minerals can be dated relative to it by the Ar technique (e.g. However, while it is often easy to determine the age of the primary standard by the K/Ar method, it is difficult for different dating laboratories to agree on the final age.
Laser probes also allow multiple ages to be determined on a single sample aliquot, but do so using accurate and precise spatial control.Instead, the ratios of the different argon isotopes are measured, yielding more precise and accurate results.Additional advantages of the single isotopic measurements of the K.The monitoring of the interfering reactions is performed through the use of laboratory salts and glasses.For example, to determine the amount of reactor produced Ar ratio of the glass is then measured in the mass spectrometer to determine the correction factor that must be applied to the rest of the samples in that irradiation.