It may well be that it is not chamber music that immediately comes to mind when you think of Sibelius. That's fair enough but he certainly wrote pieces for chamber groupings. There are, for example some single movements for quartet composed when he was a young man. Then comes this A minor quartet of 1889 and there's at least one other apart from the B flat quartet known as Voces Intimae. There are also a few pieces for strings and piano like the Piano Trio of 1884.