The Collaborative International Dictionary
Dice coal
Dice \Dice\ (d[imac]s), n.; pl. of Die. Small cubes used in gaming or in determining by chance; also, the game played with dice. See Die, n.
Dice coal, a kind of coal easily splitting into cubical
fragments.
--Brande & C.
Wiktionary
dice coal
n. (context dated English) A kind of coal that easily splits into cubical fragments.