geochronometer

1. Any of several techniques used to measure the age of rock, especially any technique of radiometric dating, the measuring of the relative abundance of particular radioactive or radiogenic isotopes in order to evaluate the progress of radioactive decay.

   Geochronometer

2. Any of several crystalline minerals that remain stable over geologic time and that when formed contained radioisotopes whose abundance relative to their decay products can be measured to calculate the age of the crystal (and thus that of the surrounding rock).

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