Across
- 3. Sun renewable power
- 6. Black rock fuel
- 8. Earth's heat energy
- 12. Conductive red metal
- 14. Organic fuel material
- 16. Renewable air energy
- 17. Nuclear fuel element
- 18. Harvested tree wood
- 19. Low-grade brown coal
Down
- 1. Invisible fossil fuel
- 2. Essential liquid resource
- 4. Fertile growing layer
- 5. Mineral-rich rock
- 7. Oil/gas bearing rock
- 9. Underground water layer
- 10. Forest building material
- 11. Aluminum source ore
- 13. Decayed plant fuel
- 15. Fossil fuel liquid
- 18. Rich upper soil layer