These are done to establish if the chemistry and minerology etc are interesting enough to see if they should consider taking a rock core from this site. They have already collected 20 of the 38 samples they can take, so they only have space for 18 more samples, so they have to choose wisely. We know they will take a sample from this region, but it could be at another site, it all depends on how hard the rock is and the results of the chemistry etc