As suggested in a comment, this is Dune Roller by Julian May, which was also the answer to Short story involving pieces of orange glass that seek out each other and defend themselves with heat.
The scene you remember with the desk is:
An odor of burned wood hit his nostrils. He exclaimed shortly under his breath and shone the light down near the sill of the outside door. There was a round black hole in the door, smoking and glowing faintly around the edges.
He raced back into the workroom and pulled out the drawer that had held the grapefruit-sized drop. It was empty, and a hole gaped in the bottom of it. The hard wood, was still burning slowly.