Scifi novella about humanoids who can walk through solid rock. Read in 1980s.

[Lynn]

The story in question is set in a mine where it is discovered there are humanoids who move about in the solid rock. It, I believe, is pre 1970s work. I read it in a collection of stories when I was in college in the 80s.

[beichst]

This is most likely The "Microscopic Giants" first published in Thrilling Wonder Stories, October 1936 (available at the Internet Archive); reprinted in Startling Stories, May 1948 (also available at the Internet Archive), and in several anthologies; . A brief portion of a review by Everett F. Bleiler in Science-Fiction: The Gernsback Years is below. You may recognize the story from it. One of the parts I remember from reading it was that they saw the humanoid wearing what appeared to be "high altitude" gear. I.e. that is why they speculated the creature was from a lower depth with even greater pressure.

In another scene--light spoiler--when the the humanoid creature is trying to retrieve/take an item with it back 'down' it uses a small flashlight device and disintegrates part of the wall.

Does any of that sound familiar?

https://www.isfdb.org/cgi-bin/title.c...

"As the faint, luminous spot in the concrete grew larger it also took on recognizable form. And the form that appeared in the depths of the stuff was that of a human!

Human? Well, yes, if you can think of a thing no bigger than an eighteen-inch doll as being human.

A mannikin a foot and a half high, embedded in the concrete! But not embedded—for it was moving! Toward us!"

[Kris]

Goodreads link for Brad's suggestion - The Microscopic Giants by Paul Ernst.

Google Books preview:
https://books.google.com/books?id=3kh...

Quote from the book:
- I can close my eyes and see the thing now: a manlike little figure walking toward us through solid concrete. It bent forward as though shouldering a way against a sluggish tide, off a heavy wind; it moved as a deep-sea diver might move ...