Gabbro igneous rock probably formed from molten material that cooled (1) rapidly at earth’s surface (2) slowly at earth’s surface (3) rapidly, deep underground (4) slowly, deeply underground
The most similar igneous rock, gabbro, formed from molten material that cooled slowly, underground (4). Gabbro found under the thin layer of basalt that makes up the top of the earth’s crust. Basalt is found on the surface of the earth’s crust because volcanic rock cools rapidly. The rock under basalt takes longer to cool and the grain is not as fine as basalt grain. This is because lava cools more slowly; therefore, larger crystals have time to grow.
Slowly, Gabbro’s subterranean igneous rock is coarse-grained and non-vesicular. Both characteristics show that it is an intrusive igneous rock. Intrusive igneous rocks form below the Earth’s surface and slowly (because they are underground). When the rocks are intrusive, they are not vesicular (no air pockets) because the air has had time to escape due to the slow cooling period. Intrusive rocks are also thick because the crystals have had time to form in the rock during this longer cooling time. Ps. Extrusive igneous rocks form rapidly on the Earth’s surface and have basically opposite characteristics for opposite reasons (eg vesicular because the air has had little time to escape)