Final answer:
Igneous and metamorphic rocks can be dated using radiometric decay methods to determine their formation times, whereas sedimentary rocks are not typically dated using this method.
Step-by-step explanation:
The kinds of rocks that can be dated using radiometric decay are primarily igneous and metamorphic rocks. Igneous rocks can be dated to determine when the minerals crystallized from magma. Metamorphic rocks can be dated to find out when the rocks were metamorphosed; however, some isotopes are not affected by metamorphism, which allows geologists to determine when the protolith, the original rock, formed before it became metamorphosed. Sedimentary rocks are not typically dated using radiometric techniques because the radiometric age would only tell you when the minerals within them crystallized in their original form, not when the sedimentary rock itself was formed. To date sedimentary rocks, geologists combine relative dating techniques with radiometric dating of cross-cutting igneous or metamorphic events.