: : You can probably add about 3-4,000 years to your time estimate. The Dwarves awoke soon after the Elves, if the Petty-dwarves really reached Beleriand first. Your time estimate only goes back to the beginning of the First Age of the Sun, but Khazad-dum was already ancient by the time the sun first rose.

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: Thanks MM. I looked up Khazad-dum in my texts but the best I could come up with was pre-First Age. Since I wanted hard numbers, I jsut went with First Age to Balrog. But that woudl definately aid in Gimli's quote about a perhaps no more then a single chip in a day.

: -RobRoy

IMO I think you are being too literal, it is doubtful that the Dwarves would dig into solid mountain, more expand (as others have suggested) a natural cave system. I also think Durin DID see the crown in the mirrormere, Gimli certainly did. Placed there as it was close to an ideal cave sytstem for a mountain fortress, not randomly.
Not withstanding this, the dwarves would have expanded and enlarged the caverns and fissures for their own ends, and it would still require thousands of dwarves working for thousands of years 'chip by chip'. They were however I believe beautfying, functionallising and connecting as opposed to hewig out bare caverns. Where for example would they all have lived for the first few hundred years if there was no cave system?
In terms of their food (which cropped up elsewhere - underground fungi, herds of edile mountain ox/cattle/goats etc. Crops nearby, underground lakes for fish.
Seems to me,Aule would have put the vision of the crown near an ideal home, both cave system and edible ecolcgy, pluys defensive position etc. etc.
IMHO
Dave