I have a micro-sd card. When it is inside my android phone and I connect it to my mac, I can read and write on it. The same happens when I put micro-sd card in the normal sized sd card adapter, and I put it in an external card reader/writer. But, this does not happen, when put micro-sd card in the normal sized sd card adapter,and I put it in my mbp slot. I can see the contents, I can read, but I cannot write or delete anything! The 'lock' slide is 'unlocked', just to mention. I also tried with disk utility, but it has no effect. It cannot even erase it or format it. Nothing at all. Other sd cards, without adapters, can be normally written when I put them in mbp sd slot. But not those used with adapter. Why this happens? Can you please test it if your mac have the same behavior? Am I forced to use external third party sd reader/writer for use with micro-sd with adapter, when my mac has sd slot? I think this is silly.