Gabbro is not an unusual rock; however, there are some qualities of gabbro that make it, like any other variety of rock, unique and individual.
First, gabbro is intrusive and coarse-grained. This means that it formed over a very long period of time, deep within the earth. It is also dark-colored, which suggests it was made of magma, rather than lava. Another quality of this interesting rock’s composition is the fact that it is an igneous rock, made mostly of the minerals plagioclase and augite. It is also the most abundant rock in the oceanic crust, which makes it relatively common.
Why is gabbro usually such a dark color? Its black to extremely deep green coloring is due to its composition of calcium-rich plagioclase feldspar and clinopyroxene .The plagioclase feldspar is usually labradorite or bytownite and the clinopyroxene is augite. Sometimes, small amounts of olivine or orthopyroxene can also be found within the rock, which may give it some lighter colored mineral grains as well. What makes gabbro unusual amongst other igneous rocks is that it often contains very little to no quartz, which is normally present in large quantities in such rocks.
What is gabbro similar to? The answer is basalt. Basalt is often mistaken to make up the oceanic crust because its composition is so much like gabbro. However, only a thin layer of the oceanic crust is actually the smaller-grained, extrusive basalt, while the intrusive gabbro, which has much larger grains, makes up the rest.
Is gabbro only found in oceanic crust? Absolutely not! The rock is also present in continental crust, where it can be discovered within thick lava flows, where cooling is extremely slow, resulting in the large grains.
How is gabbro used? There are many answers to this interesting question. Gabbro can be polished to a beautifully brilliant black luster, which is then often treasured for its versatility and excellent resistance to weathering. It is often used for counter tops in kitchens, and makes splendid floor tiles as well. Paving stones may also be made from gabbro, which is often nicknamed “black granite” for its color and resemblance.
Lastly, gabbro is a valuable ore, besides being simply a good choice for rocky furnishings. When gabbro contains some small amounts of relatively rare metals, such as the mineral ilmenite and titanium, it can be mined for human use. Some gabbro rocks can also end up yielding nickel, platinum or chromium.