Gabbro is an igneous rock which has crystallized deep in the Earth. Since the rock cooled and hardened (and crystallized) deep below
the Earth’s surface, it will be coarse grained. High pressure is usually found deep below the surface of the earth. Here, molten material cools very slowly.
The igneous rocks produced have large crystals.
Gabbro has the same mineral composition as basalt (olivine and pyroxene with smaller amounts of feldspar and mica). Whether
basalt or gabbro forms depends upon the cooling rate of the magma, not the composition of the magma. Gabbro is coarse grained
while basalt is fine grained.
Gabbro is sometimes called “black granite” for it too is coarse- grained, but a large proportion of iron-bearing minerals
make gabbro heavier and dark colored. Gabbro can also be grey or light green.
• Gabbro is widely used as crushed stone for concrete aggregate, road base material, and railroad ballast. Smaller quantities
are cut and polished for dimension stone and called black granite.
Uses of Gabbro

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