ssd won't mount

Create a bootable Knoppix Linux USB drive using Etcher (Mac/Windows/Linux). Option Boot the Knoppix USB drive and select the orange icon labeled "EFI". Open a terminal app (the black icon on the bottom left of the Taskbar near the "Start" menu).

Run the following command to get the drive ID for your Crucial SSD or you can use the GSmartControl app which is located "Start Menu --> System Tools --> GSmartControl" to get the drive ID.

sudo  lsblk  -o  NAME,FSTYPE,LABEL,SIZE,MODEL

To confirm you are using the correct drive identifier, run this command making sure to substitute the correct drive identifier for the SSD in place of the "sdX" in the following command which should show you the Crucial MX100:

sudo  hdparm  -I  /dev/sdX  | grep  -i  model

To use the ATA Secure Erase feature built into the SSD you must issue the following two commands replacing the "sdX" with the correct drive identifier for the SSD. The first command enables the ATA Security feature and the second one initiates the hardware secure erase which can take anywhere from 20 seconds to several minutes. The security lock will be disabled upon successful completion of the secure erase.

sudo  hdparm  --user-master  u   --security-set-pass  Eins  /dev/sdX
sudo  hdparm  --user-master  u   --security-erase  Eins  /dev/sdX

If the secure erase does not complete successfully, then the drive will become locked on the next power cycle. If the secure erase does not complete successfully you can remove the security lock with the following command:

sudo  hdparm  --user-master  u   --security-disable  Eins  /dev/sdX

Besides erasing the SSD, the hardware secure erase will also reset the SSD to factory defaults which can sometimes get an SSD out of a weird state.

This procedure is best performed while the SSD is connected to an internal SATA controller or to an external e-SATA port. Doing this over USB is risky since some USB Adapters, docks, enclosures may interfere when the SSD goes offline leaving the drive permanently damaged. I have successfully performed this procedure over USB using a Crucial USB to SATA Adapter.

The SSD looks good. There is a newer firmware available for this SSD, but it only resolves a security issue when the SSD's hardware encryption features are used.

https://www.crucial.com/usa/en/support-ssd-mx100

The easiest thing is to open the Terminal app and use the command line utility "dd" to erase the beginning part of the SSD so it will appear blank. You will need to get the drive identifier for the SSD. When you ran DriveDX the drive identifier for the SSD was "/dev/disk2", but it might be different the next time you connect the SSD so double check before running the following command where you replace the "diskN" with the correct drive number:

sudo  dd  if=/dev/zero  of=/dev/diskN  bs=100m  count=10

For example if the drive identifier (or Device Path) for the SSD is "disk2" as shown in the DriveDX report, then the command you will use is:

sudo  dd  if=/dev/zero  of=/dev/disk2  bs=100m  count=10

After this see if you can erase the SSD using Disk Utility. In Disk Utility you may need to click on "View" and select "Show all devices" in order to see the SSD in the left pane of Disk Utility.

If this doesn't help, then we could try a hardware secure erase on the SSD, but it is a bit risky to perform when the SSD is connected using USB.

Run DriveDX and post the report for you Crucial SSD here using the "Additional Text" icon which looks like a piece of paper. You will also need to install the special USB driver so that DriveDX can properly communicate and retrieve the health information from the SSD. Please post the report regardless of the health shown by DriveDX.

Do you have access to a PC where you can easily connect the SSD internally or externally to an e-SATA port?

Are you trying to recover data from the SSD or are you just trying to format it again?

Is your other adapter also a Sabrent? If so, you should try another brand just to be safe. Do you have a SATA drive dock or a USB drive enclosure to try? Plugable and StarTech make good devices.

Try using a different USB to SATA Adapter, dock, or enclosure. Maybe the Sabrent enclosure is defective.

If you can boot to the Snow Leopard DVD, then you can launch the Terminal app. Use

diskutil  list

in order to get the drive identifier for the SSD and use the example command I provided previously. If you get errors about the partition map, then macOS is probably attempting to read and mount the drive. We then need to use either Windows or Linux since neither one will attempt to automatically mount the drive.

What is the exact model of your old white MacBook? You can get this information by entering the system serial number here.