How can I reformat microSD cards that were created read-only?

Solution 1:

The SD card should be unmounted before attempting format.

You will probably need to use mkdosfs

for FAT16

mkdosfs /dev/sdb2 -F16

or for FAT32

mkdosfs /dev/sdb2 -F32

Solution 2:

I have found more information on this:

SD cards have a physical lock, to write protect the card. MicroSD cards don't have the lock, but the SD adapter has it, and it can lock-unlock the card.

So, try to put the card in an adapter and slid the lock a few times, leaving it on unlocked.