Yankee visiting GP, some said, for plaster of Paris material (6)
I believe the answer is:
gypsum
'plaster of paris material' is the definition.
'gypsum' can be an answer for 'material' (gypsum is a kind of material). I'm not certain of the 'plaster of paris' bit.
'yankee visiting gp some said' is the wordplay.
'yankee' becomes 'Y' (phonetic alphabet: alpha, bravo, charlie etc.).
'visiting' means one lot of letters goes inside another.
'said' shows a homophone (sound like).
'some' sounds like 'sum'.
'y' inserted into 'gp' is 'gyp'.
'gyp'+'sum'='GYPSUM'
'for' is the link.
Can you help me to learn more?
(Other definitions for gypsum that I've seen before include "Alabaster" , "Ingredient of fertilizer" , "Mineral giving plaster of Paris" , "Kind of chalk used to make plaster of Paris" , "Ingredient of plaster of Paris" .)