What does the cryptic crossword clue "A lot of sediment one about to reveal constituent of sand (6)" mean?

The wordplay uses a charade (building blocks). SIL (synonym="SIL") + I (synonym="=one") + CA (synonym="=about, circa") = SILICA The answer is SILICA.

A lot of sediment one about to reveal constituent of sand (6)

Independent Cryptic #11864 | 23 Down | 2024-10-18 flower