Crossword Genius

Mineral on board? (5)

Ross

I believe the answer is:

emery

I'm a little stuck... Click here to teach me more about this clue!

This clue could be a double definition.

'mineral' is the first definition.
(emery is a kind of mineral)

'board?' is the second definition.
The answer and definition can be both substances as well as being singular nouns.
Perhaps they are linked in a way I don't understand?

'on' is the link.

Can you help me to learn more?

(Other definitions for emery that I've seen before include "Rock used as abrasive" , "Abrasive material" , "Dick - - , late comedian" , "Hard, grey-black mineral used as 11 down" , "Abrasive powder" .)

I've seen this clue in the Evening Standard.
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