The oceanic crust is composed mainly of diabase, gabbro, and

a. basalt.

b. quartz.

c. obsidian.

d. aquamarine.

The oceanic crust is composed mainly of diabase, gabbro, and basalt.

The oceanic crust has three layers; layer 1, layer 2 and layer 3. Layer 1 consists f unconsolidated or semiconsolidated sediments. It contains of land sediments. Layer 2 is divided into two parts; uppermost volcanic layer and finely crystalline basalt. It s thin in the mid ocean but thickens away from the ridge. The third layer consists of coarse grained gabbros and igneous rocks that have a low content of silica rocks. It also consists of diabase dikes. So the answer is letter A.