Potassium 40 argon 40 dating
The primary standard must be a mineral that is homogeneous, abundant and easily dated by the K/Ar and Ar methods.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.The individual ages from each heating step are then graphically plotted on an age spectrum or an isochron.
The monitoring of the interfering reactions is performed through the use of laboratory salts and glasses.
The monitor flux can then be extrapolated to the samples, thereby determining their flux.
This flux is known as the 'J' and can be determined by the following equation: As the table above illustrates, several "undesirable" reactions occur on isotopes present within every geologic sample.
Because this (primary) standard ultimately cannot be determined by Ar, it must be first determined by another isotopic dating method.
The method most commonly used to date the primary standard is the conventional K/Ar technique.