Book or novel about an intelligent monolith from space that crashes into a mountain

Question

An intelligent rock like monolith crashes into the side of a mountain from space. It emits either heat or radiation, the military investigates. It moves down the mountain into a lake or ocean. It can't see water, but can see the ships floating on what looks like nothing. I don't remember much more, but read it quite a long time ago, maybe in the 70s or 80s.

Answer 1

I believe you're looking for A. E. van Vogt's short story "Dormant" (1948), first published in Startling Stories, November 1948 and subsequently collected several times. You're most likely to have read it in the van Vogt collection Destination: Universe!.

Iilah (the "rock") initially landed in the water, but moved up higher which is what caught people's attention:

A broad swath had been cut through the palms on the near shoreline. They were not just down—they were crushed deep into a furrow that was already alive with grass and small growth. The furrow, which looked about a hundred feet wide, led upward from the beach to the side of a hill, to where a large rock lay half-buried near the top of the hill.

Puzzled, Maynard glanced down at the Japanese photographs of the island. Involuntarily, he turned towards his executive officer. Lieutenant Gerson.

"Good lord!" he said, "how did that rock get up there? It's not on any photographs."

The "rock" is very hot, there's radioactivity, and the military sends scientists to investigate:

An engine-room thermometer registered the rock's surface temperature at eight hundred-odd degrees Fahrenheit. The answer to that was a question that shocked Maynard.

"Why, yes," he replied, "we're getting mild radioactive reactions from the water but nothing else. And nothing serious. Under the circumstances we'll withdraw from the lagoon at once and await the ships with the scientists."

But from Iilah's point of view (not seeing the ocean) it's on top of a mountain:

He was lying on a shallow plateau near the top of a mountain. The scene was desolate beyond his memory. There was not a glint nor pressure of atomic fire—not a bubble of boiling rock nor a swirl of energy heaved skyward by some vast interior explosion.

Iilah sees ships floating in "the sky:"

In 1948 he watched the destroyer float towards him through the sky. Long before it slowed and stopped just below him, he had discovered that it was not a life-form related to him. It manufactured a dull internal heat and, through its exterior walls, he could see the vague glow of fires.

You can read the story in its initial publication at the Internet Archive.