Throw out article on volcanic matter (6)
I believe the answer is:
ejecta
'volcanic matter' is the definition.
(I've seen this before)
'throw out article on' is the wordplay.
'throw out' becomes 'eject' ('eject' can be a synonym of 'throw out'**).
'article' becomes 'a' (indefinite article).
'on' means one lot of letters go next to another.
'eject'+'a'='EJECTA'
(Other definitions for ejecta that I've seen before include "Stuff thrown" , "Volcanic matter" , "matter being thrown out" , "Material forced out by an eruption" , "Material thrown out by volcano; ace jet (anag.)" .)