Related Clues:

• Mined stuff
• Santa's 'present' for a naughty child
• Briquette
• Diamond's ancestor
• Carbon fuel
• Greenhouse gas culprit
• Old-time furnace fuel
• Hopper fill
• Anthracite or lignite
• Frosty's eyes
• Certain fossil fuel
• 'Present' in bad kids' Christmas stockings
• Ember
• "Black diamonds"
• Annual sign of bad behavior?