View your list of saved words. (You can log in using Facebook.)
In igneous petrology, the sum of the volume percentages of the coloured, or dark, minerals in the rock. The most common light-coloured minerals are feldspars, feldspathoids, and silica or quartz; abundant dark-coloured minerals include olivine, pyroxene, amphibole, biotite, garnet, tourmaline, iron oxides, sulfides, and metals.
This entry comes from Encyclopædia Britannica Concise. For the full entry on colour index, visit Britannica.com.
Seen & Heard
What made you look up colour index? Please tell us what you were reading, watching or discussing that led you here.