What causes desert varnish?

Related questions

1. How many modes are there?
2. Is Ionian the same as major?
3. Is Aeolian major or minor?
4. What is authentic mode?
5. What causes Ventifacts formation?
6. How are Ventifacts formed?
7. Where are Ventifacts found?
8. What is Aeolian cycle?
9. What is F Phrygian?
10. What are the 4 types of sand dunes?

Tags

1. #other
2. #particles
3. #found
4. #composed
5. #surfaces
6. #oxides
7. #regions
8. #black
9. #characteristics
10. #trace
11. #varnish
12. #elements
13. #desert
14. #hydroxides
15. #minerals
16. #exposed
17. #caused
18. #coating
19. #major
20. #grains
21. #manganese