Crossword Genius

Periodically the one cloth that may be used to clean up gemstone? (6)

Ross

I believe the answer is:

garnet

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

'gemstone?' is the definition.
(I know that garnet is a type of transparent gem)

'periodically the one cloth' is the wordplay.
'periodically' becomes 'gar' (I can't explain this - if you can you should believe this answer much more).
'the one cloth' becomes 'net' (net is a kind of cloth).
'gar'+'net'='GARNET'

'that may be used to clean up' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.

Can you help me to learn more?

(Other definitions for garnet that I've seen before include "Glassy red, yellow or green gemstone" , "Hard glassy mineral used as a gemstone" , "Deep red gem stone" , "Semi-precious stone of argent type" , "Deep red gemstone" .)

I've seen this clue in The Telegraph.
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