Sedimentary rock on the other hand consists of sedimentary particles which were removed and deposited somewhere else by some sort of fluid (generally wind and water).
The sedimentary particles predate the rock which they form.
Dating the particles which make up the rock wouldn’t give you the age of the rock itself.
In addition, the redeposition process upsets the conditions necessary to achieve accurate results through radiometric dating.
Lava (properly called magma before it erupts) fills large underground chambers called magma chambers.
Most people are not aware of the many processes that take place in lava before it erupts and as it solidifies, processes that can have a tremendous influence on daughter to parent ratios.
Here I want to concentrate on another source of error, namely, processes that take place within magma chambers.
Recent advances in the field of geochronology have led to a greater understanding of the scale and duration of geological processes.
It is currently possible to date igneous and metamorphic rocks by a variety of radiometric methods to within a million years, but establishing the depositional age of sedimentary rocks has remained exceedingly difficult.
Furthermore, Parentium and Daughterium are so different in chemical properties that they don't otherwise occur together.
If there were such a pair of isotopes, radiometric dating would be very simple.