Crossfire Disks come formatted for Windows or at least mine did. I had to use a Windows system to remove all the partitions before the Mac would read it. Used Disk Utility to partion it, once I did that it worked fine.
I did purchase a mac formatted drive. It had the XF code underneath.
I took your advice anyway and re-formatted for mac using Disk Utility, it then mounted fine.
Dam PCs, they get everywhere, even when you buy it mac formatted.