I tried the suggested Terminal command and got this:
Last login: Tue Jan 31 12:28:11 on ttys000
RobertscBookPro:~ robertxxx$ diskutil erasedisk hfs+ External GPT /dev/disk2
Started erase on disk2
Unmounting disk
Creating the partition map
Waiting for partitions to activate
Formatting disk2s2 as Mac OS Extended with name External
Initialized /dev/rdisk2s2 as a 465 GB case-insensitive HFS Plus volume
Mounting disk
Finished erase on disk2
RobertscBookPro:~ robertxxx$
To no avail, I still have the PARTITION icon dimmed.
This is the info of the external Samsung SSD T3
Volume name : External
Volume type : Physical Volume
BSD device node : disk2s2
Mount point : /Volumes/External
File system : Mac OS Extended
Connection : USB
Device tree path : IODeviceTree:/PCI0@0/XHC1@14
Writable : Yes
Is case-sensitive : No
File system UUID : 1B65CCC5-5FD0-34D9-AC1C-90C51234C0B0
Volume capacity : 499,763,888,128
Available space (Purgeable + Free) : 499,357,732,864
Purgeable space : 0
Free space : 499,357,732,864
Used space : 406,155,264
File count : 53
Owners enabled : Yes
Is encrypted : No
System Integrity Protection supported : No
Can be verified : Yes
Can be repaired : Yes
Bootable : No
Journaled : No
Disk number : 2
Partition number : 2
Media name :
Media type : Generic
Ejectable : Yes
Solid state : No
Parent disks : disk2
What can I do to partition the SSD?
Robert