Crystalline Igneous Rocks

If a rock is made of randomly oriented crystals of different sizes, it´s probably a plutonic igneous rock, one which cooled slowly far below the earth´s surface. Granite and granitic rocks (light-colored plutonic igneous rocks) often are made of three or more different minerals, so they are often a mixture of clear, white, pink, light gray, and a black minerals grains. Diorite and other "intermediate" (not light, not dark) rocks are often made of clear, white, and dark minerals - the dark minerals are usually a higher percentage of the total rock than you find in granites. Gabbro (dark-colored plutonic rock) will appear to be mostly dark minerals.