The answer to this question would be: Because CoCl2 will change color when humidity changes.
Cobalt chloride or CoCl2 can change its color depends on the humidity. The dry cobalt chloride will have pink color but it will changes into blue if you mix it with water. If the humidity is high, the water in the air might condense into the cobalt chloride and change its color to blue. So high humidity will cause more cobalt chloride turn into blue.
Answer:
Sift the mixture to separate the rock from the iron filings, soil and salt.
You can then use a magnet to separate the iron filings from the salt and soil.
Afterwards, you can pour water into the remaining salt- soil mixture. Salt will dissolve but the soil will remain at the bottom of the water.
If you want to separate the salt from the water, you can boil it till all the water evaporates. The only thing that'd be left in the pan is salt.