sentence2_structure: Gabbro<>is<>a dark dense rock that can be found in the oceanic crust$$$a dark dense rock<>can be found<>in the oceanic crust
sentence1: Continental crust is much older, thicker and less dense than oceanic crust.
sentence2: Gabbro is a dark dense rock that can be found in the oceanic crust.
question: Gabbro is a dark dense rock that can be found in what?