What is the hardest substance on earth?

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Tags

1. #meteorites
2. #harder
3. #lonsdaleite
4. #hardest
5. #substance
6. #earth
7. #nitride
8. #wurtzite
9. #naturally
10. #diamond
11. #found
12. #which
13. #comes
14. #occurring
15. #boron
16. #synthetic