The most common and most likely answer to this crossword clue is the 7 letter word REALGAR
I've seen this crossword clue in The Daily Telegraph
R
E
A
L
G
A
R
More clues leading to the result REALGAR
- Genuine fish pigment
- Genuine garnet but not clear mineral
- Pigment made from genuine fish
- Substantial domestic plot — study extracted mineral
- Mineral not fake guy brought up
- Mineral water at last needed by a cracking composer
- Rosaker — a genuine paperback
- It's true — paper back is a source of poison
- Genuine fish, could be poisonous
- Authentic fish pigment
Buddy explains!
The straight part
We know that "Mineral" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case mineral = realgar.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 REALGAR mean?
REALGAR noun- A mineral, arsenic sulfide (AsS), often associated with orpiment and stibnite in lead, silver and gold ores.