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