Jamieson, Fausset and Brown on 1 Chronicles 20:2

2. David took the crown of their king ..., and found it to weigh a talent of gold--equal to one hundred twenty-five pounds. Some think that Malcom, rendered in our version "their king," should be taken as a proper name, Milcom or Molech, the Ammonite idol, which, of course, might bear a heavy weight. But, like many other state crowns of Eastern kings, the crown got at Rabbah was not worn on the head, but suspended by chains of gold above the throne.

precious stones--Hebrew, a "stone," or cluster of precious stones, which was set on David's head.