The most common and most likely answer to this crossword clue is the 8 letter word FLUORITE
I've seen this crossword clue in Financial Times
F
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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 FLUORITE mean?
FLUORITE noun- A widely occurring mineral (calcium fluoride), of various colours, used as a flux in steelmaking, and in the manufacture of glass, enamels and hydrofluoric acid.