Explore excavation obtaining a large gem (10)
I believe the answer is:
tourmaline
'gem' is the definition.
(tourmaline is a kind of gem)
'explore excavation obtaining a large' is the wordplay.
I cannot quite see how this works, but
'a' is present in the answer.
'large' could be 'l' (eg in clothes sizes) and 'l' is found in the answer.
'excavation' could be 'mine' (mine is a kind of excavation) and 'mine' is found within the leftover letters.
The remaining letters 'tour' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for tourmaline that I've seen before include "Beautiful blackish mineral" , "Beautiful grey or black mineral" .)