Crystalline rock

I think it could be either:

Which length description are you looking for?:

schist

'crystalline rock' is the definition.
(I've seen this in another clue)

This is all the clue.

(Other definitions for schist that I've seen before include "layered rock" , "Coarse-grained rock" , "Form of rock" .)

I've seen this clue in The New York Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.