Power Grid Coal Pile Piece

This is a replacement oil barrel for the board game "Power Grid" by Friedmann Friese and Rio Grande Games.
This is the piece that I dislike the most in the base game. It's a brown wooden cube. So I wanted to create a piece that more closely reflects the game's art for the coal resource, namely a large pyramidal pile.
I am not quite satisfied with the look of this piece on account of how it looks more like a pile of cannon balls than anything else.