The rock, depending on which kind, metaphoric, sedimentary, or igneous, most likely igneous, the volcanologist can determine the age of the rock. The age of the rock says how long it has been in the volcano, for example, diamond is made in a volcano, finding how old it makes it rarer, and expensive and adds a lust to it too. Therefore, How old the rock is can determine how old approximately the volcano can be.
