Black-hearted crystalline compound snaps here? (5)
I believe the answer is:
album
'snaps here?' is the definition.
(a photo album contains snaps)
'black-hearted crystalline compound' is the wordplay.
'black' becomes 'b' (as in pencil classifications).
'hearted' indicates putting letters inside (some letters go to the heart of the word).
'crystalline compound' becomes 'alum' (alum is a chemical compound).
'b' inserted into 'alum' is 'ALBUM'.
(Other definitions for album that I've seen before include "Music record or photo book" , "LP, perhaps?" , "LP, CD; blank book" , "Book for stamps/photos" , "Item of music released" .)