China has been by far the biggest coal producing country over the last three decades. The country produced about 3.6 billion tonnes (Bt) of coal in 2012 accounting for over 47% of the world's total coal output.
Explanation: Splitting the diagram in half horizontally and vertically, each quarter contains the alphabet written in sequence, with the relative position of this sequence rotating 1/4 turn anti-clockwise as you move clockwise around the quarters.