Stony 'Mr' from Margate (5)
I believe the answer is:
agate
'stony mr from margate' is the definition.
I can't judge whether this definition defines the answer.
'mr from margate' is the wordplay.
'from' is a deletion indicator.
'margate' with 'mr' removed is 'AGATE'.
Can you help me to learn more?
(Other definitions for agate that I've seen before include "Decorative stone" , "Quartz variety" , "Banded ornamental stone" , "Semi-precious stone" , "Impure form of quartz with banded chalcedony, used as a gemstone" .)