The most common and most likely answer to this crossword clue is the 6 letter word JASPER
I've seen this crossword clue in The Daily Telegraph
J
A
S
P
E
R
More clues leading to the result JASPER
- What’s central to Beijing, according to China
- What’s held by raja’s perfect gemstone
- Agreed to a German weapon after it’s cut a gemstone
- It’s a gemstone, according to past head of jewellery
- Judge, according to Stone
- Quartz extracted from Abuja’s perfect
- Gemstone‘s origin found in jeweller’s, typically
- Little James: a jewel
- Joker swallows small stone
Buddy explains!

The straight part
We know that "Quartz" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case quartz = jasper.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 JASPER mean?
JASPER noun- Any bright-coloured kind of chalcedony apart from cornelian.
- An opaque, impure variety of quartz, of red, yellow, and other dull colors, breaking conchoidally with a smooth surface.
- Jasperware pottery.
- A wasp.
- A person, a guy, especially seen as naïve or simple.