The most common and most likely answer to this crossword clue is the 9 letter word ALABASTER
I've seen this crossword clue in The Times
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More clues leading to the result ALABASTER
- Smooth and white, a plant undergoing tests?
- White substance provided as one preparing joint?
- After black, flower is white
- White flower, one created by boffins?
- Sculptors work with this muscle when involved in recast
- What’s used for carving in the manner of turkey roaster
- Mineral article absorbed by metal kitchen implement
- A dog getting flower and stone
- One who reprimands Mark goes very pale
- Are basalt rocks gypsum?
Buddy explains!

The straight part
We know that "White substance" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case white substance = alabaster.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 ALABASTER mean?
ALABASTER noun- A fine-grained white or lightly-tinted variety of gypsum, used ornamentally.
- A variety of calcite, translucent and sometimes banded.
- An off-white colour, like that of alabaster.
- Made of alabaster
- Resembling alabaster: white, pale, translucent.