Rocks are naturally occurring solids which are composed of minerals & have been used by humans since ages. From Stone Age, rocks are used for various purposes. Also, the metals and minerals found in rock play an important role in our life. Get to know all the Coal Uses. We have provided you with all information about Coal rock here. Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers called coal beds. Coal is available in black, brown, dark brown, grey, light to dark grey colors. The streak of a rock is the color of powder produced when it is dragged across an unweathered surface. The streak of Coal is black. Get to know more about Coal rock and characteristics of Coal rock in the next sections.