Sort of club for stony members? (5)
I believe the answer is:
slate
'sort of club' is the definition.
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for slate that I've seen before include "Scold; hard rock" , "rock used in building" , "Criticise harshly" , "Roofing plate" , "Stone used for roofing" .)