The most common and most likely answer to this crossword clue is the 6 letter word AGATES
I've seen this crossword clue in The Guardian
A
G
A
T
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S
More clues leading to the result AGATES
- A fixed silver mounting for gemstones
- An entrance's variegated stones
- A billionaire’s gems
- Is a stirrer losing it – and marbles?
- Marbles provided by a wealthy American philanthropist
- Playing sage at marbles
- Stones put up to support cooker
- Semi-precious stones and silver corroded by sulphur
- Precious stones, as seen framing entrance
- Stones showing range with group making comeback
Buddy explains!

The straight part
We know that "Semi-precious stones" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case semi-precious stones = agates.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 AGATES mean?
AGATES noun- A semi-pellucid, uncrystallized variety of quartz, presenting various tints in the same specimen, with colors delicately arranged in stripes or bands, or blended in clouds.
- The size of type between pearl and nonpareil, standardized as 5 1/2-point.
- One fourteenth of an inch
- A diminutive person; so called in allusion to the small figures cut in agate for rings and seals.
- A tool used by gold-wire drawers, bookbinders, etc.;—so called from the agate fixed in it for burnishing.
- A marble made from agate.
- (usually in the plural) A testicle.