How do I format a partition with FAT32?
Enter diskutil list to get the disk identifier/partition. Then enter:

diskutil eraseVolume FAT32 DATA diskXsY #replace diskXsY by the proper disk identifier


DATA will be the name of the volume. The name has to be capitalized using diskutil ....



The diskutil eraseVolume ... command will change the pMBR of the GUID partition table to a hybrid MBR and probably renders an existing OS X system volume on the same drive unbootable.