How can I reformat a drive that contains an encrypted volume? After OS X 10.7 came out with its disk-encryption features, I encrypted an empty USB thumb drive just for grins. I never used it, and eventually decided to reformat it as a normal drive for use with Windows and earlier versions of OS X.

When I opened Disk Utility to try to erase and repartition the drive, however, things looked weird. I clicked on the drive in the left sidebar, but there was no “Erase” tab on the right—only “First Aid” and “Partition”—and the “Partition” tab said, “You may only split this partition into two. To do this, click +.” There was no option to change the partition layout or to remove the encryption from my volume. How can I reformat this drive to remove the encryption?
It turns out that Disk Utility didn’t want to touch a disk that contained an encrypted partition, but it had no issue with changing the encrypted partition itself. I clicked on the encrypted partition (not the drive) in the sidebar, and the “Erase” tab appeared on the right. From there I reformatted the disk to Mac OS Extended without encryption, and afterward Disk Utility had no hangups about reformatting or repartitioning the drive.