The most common and most likely answer to this crossword clue is the 10 letter word TOURMALINE
I've seen this crossword clue in The Daily Telegraph
T
O
U
R
M
A
L
I
N
E
More clues leading to the result TOURMALINE
- Travel round African country, northeastern gem
- Explore excavation obtaining nearly every gem
- Go around northernmost place in Ireland — finally locate valuable mineral
- Explore excavation obtaining a large gem
- Turn out mineral to produce gemstone
- Go round Irish head — finally see beautiful mineral
- Trip with graduate to Nile failing to get mineral
Buddy explains!
The straight part
We know that "gemstone" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case gemstone = tourmaline.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TOURMALINE mean?
TOURMALINE noun- A complex black or dark-coloured borosilicate mineral, compounded with various chemical elements and considered a semi-precious stone.
- A transparent gemstone cut from it.