Joined Mr Gore for a mineral (5)
I believe the answer is:
metal
'a mineral' is the definition.
The definition and answer can be both substances as well as being singular nouns.
Maybe there's a link between them I don't understand?
'joined mr gore' is the wordplay.
'joined' becomes 'met' (meeting is a kind of joining).
'mr gore' becomes 'Al' (US politician Al Gore).
'met'+'al'='METAL'
'for' acts as a link.
Can you help me to learn more?
(Other definitions for metal that I've seen before include "Musically it can be heavy" , "Copper, perhaps" , "barium?" , "lead as one" , "Like steel cutlery" .)