I formatted an SD Card as ext4 on my Debian machine. Before I formatted I deleted all partions, created a single partion, and write the changes.
I was able to mount the SD card on my Debian box and it worked fine. I created a directory and unmounted.
When I tried to use the card on my iMac (El Capitan) the SD card wouldn't appear in Finder or Disk Utility.
I downloaded FuseForOSX and installed. And still it's not showing the SD Card in Finder. If I move the SD card over to my Debian machine it will mount just fine.
Any ideas what's going wrong?