This follows on from my previous question about Mordor.
What was so special about Mount Doom for Sauron to decide to use this place to forge the One Ring? I am under the impression that Mount Doom was more than just a volcano (or Mountain of Fire, as it's never explicitly called a volcano).
This thread suggests that Mount Doom was the only volcano/mountain of fire in Middle Earth. Is this true? Is there anything that backs up this claim?
I am assuming that Mount Doom was already in place before Sauron decided to settle in Mordor. For Sauron it may have been the deciding factor in selecting his new home, as it was where he forged the Ring of Power.
This answer states that Mount Doom had magical significance, but I struggle to find any explanation or source of this significance.
Was there any connection between Mount Doom and Utumno, Angband or Morgoth himself?
This answer suggests that "volcanoes were remainders of the doings of Melkor (Morgoth) in his attempts to undo the work of the Valar in the days before the reckoning of time". So if Morgoth was responsible for all volcanoes, what made Mount Doom so special?
As a child I was under the impression that Morgoth's final resting place was Mount Doom, and hence its special significance. But researching into this as an adult I can find no reference to this happening, so I'm not sure where I got this idea from.