The right option is; its mineral content
Mineral content is the property of the rock that gives the rock its dark color.
Minerals are the building blocks of rock and rocks mainly derive their colors from them. Most rocks contain various types of minerals that are joined together while few rocks contain just a type of mineral. Rocks that their mineral constituent is pyroxenes, olivines or amphiboles are usually dark in color while rocks that have much of feldspar and quartz are usually light in color.
