“Black granite” is commonly seen in commercial rock, but it is not granite at all. As said above, granite must be at least 20% quartz, which means an all-black rock is not granite. Most commonly, black granite is in fact gabbro, a mafic intrusive igneous rock similar to basalt. Gabbro is primarily composed of minerals pyroxene, plagioclase, and small amounts of olivine (dark green) and amphibole.
Black granite is actually gabbro rock, an igneous stone similar to basalt. It primarily contains plagioclase and pyroxene minerals. There are also amphibole and olivine minerals.