煤 'coal' + 块 'lump/block.' Pattern: any solid in lump form takes 块 - 冰块 'ice cube,' 石块 'rock chunk.' So 煤块 is just 'coal lump.'
culture
In 煤球 'coal-ball' style, urban North China households burned hand-pressed honeycomb briquettes (蜂窝煤) for cooking and heating into the 1990s. 煤块 covers both these formed briquettes and raw mined chunks.
