The most common and most likely answer to this crossword clue is the 10 letter word BLOODSTONE
I've seen this crossword clue in The Times
B
L
O
O
D
S
T
O
N
E
Buddy explains!
The straight part
We know that "Mineral found in veins?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case mineral found in veins? = bloodstone.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 BLOODSTONE mean?
BLOODSTONE noun- A green chalcedony that has been sprinkled with red spots (which resemble blood, hence the name).
- Hematite.