Turning up in drinking vessel, notice mineral (6)
I believe the answer is:
gypsum
'mineral' is the definition.
(gypsum is a kind of mineral)
'turning up in drinking vessel notice' is the wordplay.
'turning up' says the letters should be written backwards.
'in' means one lot of letters goes inside another.
'drinking vessel' becomes 'mug' (mug is a kind of drinking vessel).
'notice' becomes 'spy' (I've seen this before).
'mug' placed around 'spy' is 'muspyg'.
'muspyg' backwards is 'GYPSUM'.
(Other definitions for gypsum that I've seen before include "Spy mug made from this white mineral" , "Mineral used in making plaster of Paris" , "Mineral used to make plaster of Paris" , "Kind of chalk used to make plaster of Paris" , "Mineral giving plaster of Paris" .)