Can't format USB with Disks in Ubuntu 18.10

Question

I think I have a broken USB.
It won't show up in the File manager and even not in GParted, just in the Disks Application preinstalled in Ubuntu 18.10.
It says, that the stick is mounted on /dev/sdb but if I try to cd into that directory with the Terminal, it won't work. And if I want to format it with the Disks Application, I can't! The option is greyed out! I can just click on "Edit Mount Options..." Could someone please help me?