The knife will not scratch the quartz, but will mark felspar and easily pick off flakes of mica. One has to be careful to see that it is the rock being scratched and not the knife. Use the point only. There are many interesting minerals to find and the job gets even more complicated the nearer you get to the Esterels. Their is even a unique rock to be searched for between Bouloris and Dromont, near St. Raphael - the beautiful dark blue 'Esterillite'.
Minerals are what rocks are composed of.
They, themselves, are made up of oxides or carbonates.