White chemical substance derived from Asian gem (8)

I believe the answer is:

magnesia

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'white chemical substance' is the definition.
'magnesia' can be an answer for 'substance' (magnesia is a kind of substance). I'm not certain of the 'white chemical' bit.

'derived from asian gem' is the wordplay.
'derived from' indicates an anagram.
'asian'+'gem'='asiangem'
'asiangem' anagrammed gives 'MAGNESIA'.

Can you help me to learn more?

(Other definitions for magnesia that I've seen before include "laxative" , "Asian gem (anag) - milk of ___" , "Carbonate used as an antacid" , "Is Ma easing off the white mineral?" , "Medicinal powder" .)

I've seen this clue in The Hindu.

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