One of the ways in which the different substances are classified and identified is called the scratch test- which involves testing their hardness.

The scale was devised by Friedrich Mohs. He was a 19th Century German Mineralogist. The scale known as Mohs scale of harness had ten grades in all.

Minerals of each grade can scratch all the minerals of lower grades. They will get scratched by the minerals of the higher grade.

The ten grades in their increasing order of hardness is as follows :-

1. Talc.

2. Gypsum (rock salt).

3. Calcite.

4. Fluorite.

5. Apatite.

6. Orthoclase feldspar.

7. Quartz.

8. Topaz.

9. Corundum.

10. Diamond.

11. Gold…….2.5 to 3.0

12. Silver ….2.0 to 3.0

13. Platinum..4.0 to 4.5

14. Emeralds and aquamarines…7.5 to 8.0

15. Sapphires and rubies…9.0

16. Amber….2.0 to 2.5

17. Amethyst…7.0

18. Garnet…..6.5 to 7.5

19. Jade………6.5 to 7.0

20. Lapis lazuli…5.5

21. Malachite….3.5 to 4.0

22. Moonstone…..6.0

23. Opal…..5.5 to 6.5

24. Tiger’s eye….4.0

25. Tourmaline 7 to 7.5

26. Turquoise…6.0

27. Graphite..1.0 to 2.0