Idea of Coal Icon
The icon is a very jagged rock. Three facets are visible, forming a jagged triangle, quadrilateral and a pentagonal facet. The outside is also very angular and possessing of six uneven sides. The icon represents coal, a dark substance harvested from the earth in order to use for power generation.
This page shows the different variations of the Coal from an Icons8 icon pack. Feel free to resize and recolor the icon, and then download the icon in PNG format for free.