A tech billionaire collected such stones (6)
I believe the answer is:
agates
'stones' is the definition.
(I've seen this before)
'a tech billionaire collected' is the wordplay.
I cannot really see how this works, but
'a' is present in the answer.
'billionaire' could be 'gates' (tech billionaire Bill Gates) and 'gates' is found in the answer.
No letters remain.
This explanation may well be incorrect...
'such' is the link.
Can you help me to learn more?
(Other definitions for agates that I've seen before include "marbles" , "Name for stones" , "Banded semiprecious stones" , "Set aga up for shiny stones" , "Multi-coloured quartzes" .)