Crystalline rock (5)

I think it could be either:

Which length description are you looking for?:

geode

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

This is all the clue.

(Other definitions for geode that I've seen before include "Druse" , "Small rock cavity" , "Crystal-lined cavity in rock" .)

I've seen this clue in the Newsday.

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