USB Storage Device Mounts but is not visible in finder.

UPDATE: I was able to get the drive recognized by the OS (Sierra 10.12.6). In Finder preferences, I noticed there wasn't a check next to "External Disks". After checking it, the drive appears. But yet, still not displaying the files contained on the drive. Suggestions?

Thanks again.

It is the original 500GB bootable hard drive from the machine. Wouldn't that be Mac OS Extended (Journaled)?

Confirmed via Disk Utility: Mac OS Extended Journaled.

(Thank you for your continued attention to my problem).

I've cut and pasted the results of the "diskutil info /" command you've asked me to execute. But it would seem that the info returned is only on the 1TB SSD drive I installed as a replacement to the original 500GB drive.

It is the 500GB drive that I am able to mount but cannot see any files.

Is there a way to point to the external drive in question?

diskutil info /

   Device Identifier:        disk0s2

   Device Node:              /dev/disk0s2

   Whole:                    No

   Part of Whole:            disk0

   Volume Name:              SAMSUNG SSD

   Mounted:                  Yes

   Mount Point:              /

   Partition Type:           Apple_HFS

   File System Personality:  Journaled HFS+

   Type (Bundle):            hfs

   Name (User Visible):      Mac OS Extended (Journaled)

   Journal:                  Journal size 81920 KB at offset 0x1d1c000

   Owners:                   Enabled

   OS Can Be Installed:      Yes

   Recovery Disk:            disk0s3

   Media Type:               Generic

   Protocol:                 SATA

   SMART Status:             Verified

   Volume UUID:              2643281B-2032-39AD-86B5-C0D2E0EA69D0

   Disk / Partition UUID:    D5661BFF-A852-468B-B485-415E5A753A99

   Disk Size:                999.3 GB (999345127424 Bytes) (exactly 1951845952 512-Byte-Units)

   Device Block Size:        512 Bytes

   Volume Total Space:       999.3 GB (999345127424 Bytes) (exactly 1951845952 512-Byte-Units)

   Volume Used Space:        224.9 GB (224926543872 Bytes) (exactly 439309656 512-Byte-Units) (22.5%)

   Volume Available Space:   774.4 GB (774418583552 Bytes) (exactly 1512536296 512-Byte-Units) (77.5%)

   Allocation Block Size:    4096 Bytes

   Read-Only Media:          No

   Read-Only Volume:         No

   Device Location:          Internal

   Removable Media:          Fixed

   Solid State:              Yes

The ignore permissions box was already checked when I went into the Get Info option.

The drive appears in the side bar but the files on the drive still are not visible.

Ok... so what is my next step short of putting the drive back in the machine to take files off the drive?

So, I've been doing some thinking on this...

Is it possible that the drive knows it has been removed from the machine and is unreadable outside the MacBook?