Radioactive dating using potassium argon
This technique is used on ferromagnesian (iron/magnesium-containing) minerals such as micas and amphiboles or on limestones which also contain abundant strontium.
However, both Rb and Sr easily follow fluids that move through rocks or escape during some types of metamorphism. The dual decay of potassium (K) to 40Ar (argon) and 40Ca (calcium) was worked out between 19.
The isotopes are then measured within the same machine by an attached mass spectrometer (an example of this is SIMS analysis).
This is a common dating method mainly used by archaeologists, as it can only date geologically recent organic materials, usually charcoal, but also bone and antlers.
Radioactive decay is a natural process and comes from the atomic nucleus becoming unstable and releasing bits and pieces.
This method faces problems because the cosmic ray flux has changed over time, but a calibration factor is applied to take this into account.
This technique uses the same minerals and rocks as for K-Ar dating but restricts measurements to the argon isotopic system which is not so affected by metamorphic and alteration events. The decay of 147Sm to 143Nd for dating rocks began in the mid-1970s and was widespread by the early 1980s.
It is useful for dating very old igneous and metamorphic rocks and also meteorites and other cosmic fragments.
This technique is good for iron meteorites and the mineral molybdenite.
This system is highly favoured for accurate dating of igneous and metamorphic rocks, through many different techniques.