These minerals are common to many igneous and metamorphic rocks.
Similarly, in geology, if distinctive granitic pebbles can be found in the sediment beside a similar granitic body, it can be inferred that the granite, after cooling, had been uplifted and eroded and therefore was not injected into the adjacent rock sequence.
After estimating the rate of this radioactive change, he calculated that the absolute ages of his specimens ranged from 410 million to 2.2 billion years.
Though his figures were too high by about 20 percent, their order of magnitude was enough to dispose of the short scale of geologic time proposed by Lord Kelvin. This device separates the different isotopes of the same element and can measure the variations in these isotopic abundances to within one part in 10,000.
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.