Have you ever had a SD card seem to go bad? Perhaps it’s acting flaky and there seems to be no signs of physical damage. I had just that happen with some cards that wouldn’t show up (turns out they were improperly formatted using Apple Disk Utility by an assistant being overzealous).
I found a great program that’s both free and official. It’s SD Formatter 4.0 for SD/SDHC/SDXC cards. It’s actually created by the SD Association that oversees the SD Card format. You can get it here https://www.sdcard.org/downloads/formatter_4/
This tool can format all SD memory cards, SDHC memory cards and SDXC memory cards. It ensures that the cards are fully compliant (especially for things like card speed and buffering). The association states that:
The SD Formatter was created specifically for memory cards using the SD/SDHC/SDXC standards. It is strongly recommended to use the SD Formatter instead of formatting utilities provided with operating systems that format various types of storage media. Using generic formatting utilities may result in less than optimal performance for your memory cards.
The free utility is available for Windows 8, 7, Vista, and XP as well as Mac OS X (10.910.5). Download it from their website for free https://www.sdcard.org/downloads/formatter_4/.