The most common and most likely answer to this crossword clue is the 7 letter word LEUCITE
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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 = leucite.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 LEUCITE mean?
LEUCITE noun- A mineral of silica-poor igneous, plutonic and volcanic rocks. Chemically, leucite is a potassium feldspar with insufficient silica to satisfy the chemical bonds. Because of the unfilled bonds, leucite weathers rapidly and can only be seen as inclusions in freshly broken rock.
- A leucoplast.