Regularly grout slab with mineral (6)

I believe the answer is:

rutile

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'mineral' is the definition.
Both the answer and definition are singular nouns.
Maybe there's a link between them I don't understand?

'regularly grout slab' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'slab' becomes 'tile' (tile is a kind of slab).
The alternate letters of 'grout' are 'ru'.
'ru'+'tile'='RUTILE'

'with' is the link.

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I've seen this clue in The Hindu.

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