Element of bile is ursodeoxycholic matter, initially (7)

I believe the answer is:

gallium

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'element' is the definition.
(gallium is a kind of element)

'bile is ursodeoxycholic matter initially' is the wordplay.
'bile' becomes 'gall' (I am not sure about this - if you are sure you should believe this answer much more).
'initially' says to take the initial letters.
The first letters of 'is ursodeoxycholic matter' is 'ium'.
'gall'+'ium'='GALLIUM'

'of' is the link.

Can you help me to learn more?

(Other definitions for gallium that I've seen before include "soft one" , "Metallic element" .)

I've seen this clue in The Everyman puzzle in The Observer.

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