Black rock band to start with American season (6)
I believe the answer is:
basalt
'black rock' is the definition.
(I've seen this in another clue)
'band to start with american season' is the wordplay.
'to start with' says to take the initial letters.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'season' becomes 'salt' (salt can mean to season with salt).
The initial letter of 'band' is 'b'.
'b'+'a'+'salt'='BASALT'
(Other definitions for basalt that I've seen before include "Type of rock is a blast, oddly" , "rock from 2 [VOLCANO]" , "Dark rock of volcanic origin" , "Commonest type of solidified lava; dense, dark grey and fine-grained" , "Black volcanic rock" .)