Gnome set out to find precious rock (8)
I believe the answer is:
gemstone
'precious rock' is the definition.
(precious stone)
'gnome set out' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'gnome'+'set'='gnomeset'
'gnomeset' anagrammed gives 'GEMSTONE'.
'to find' is the link.
(Other definitions for gemstone that I've seen before include "Sparkler" , "Eg, sapphire" , "Emerald or ruby" , "something of great value" , "Piece of crystalline rock as jewellery" .)