'coal-rich' originates from Modern English, specifically the compound of the words 'coal' and 'rich', where 'coal' meant 'fossil carbon fuel' and 'rich' meant 'abundant'.

'coal' comes from Old English 'col' (Middle English 'cole') and developed into the modern English word 'coal'; 'rich' comes from Old English 'rice/ric' (Middle English 'rich') and became the modern adjective 'rich'. These two elements were combined in Modern English to form the compound adjective 'coal-rich'.

Initially the elements referred separately to 'coal' and to being 'rich' or abundant; over time they combined into the compound 'coal-rich' meaning 'abundant in coal'.