Thyme sat oddly on the stone (8)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
amethyst
(Other definitions for amethyst that I've seen before include "Precious stone of purple quartz" , "Transparent bluish quartz" , "A Middle East language" , "Type of quartz" , "Purple quartz used in jewellery" .)