buit it's not the title of a book.....*retracts already abstract answer*

CdM] Was the fictional work originally written in English? Yes
Inkspot] Was the film made before 1950? No, for all versions (see below)
Darren] Is there more than one filmed version (including cinematic and television versions, if applicable)? Yes, according to IMBd three (one cinematic, two television). Obligatory trivia - the actor playing the person in the answer in the first TV version was once in Blake's seven, and also has a connection to the colour clue.
Raak] Is it an item of furniture? Yes, though that's not its primary function
ZK] Is it anything to do with Oscar Wilde, or in fact Dorian Gray, and am I allowed to ask more than one question at a time? No, and no, and apparently yes
ZK] Tom Brown's Schooldays? I refer the honourable gentleman to his subsequent answer

(For example, do you think it would be an acceptable solution in a crossword?)

CDM] Is the entire answer a phrase that is in reasonably common use? No - it'd only really be acceptable in a crossword if the whole crossword was themed around the author.

Raak] Is the author Dickens? No
Darren] Is the person male? No
ZK]Is it a musical instrument? Yes
CdM] Regarding the mineral part: (a) is it in part glass? (b) you said there are "metal fixings" but are there also other metal parts? (a) No; (b) Yes
ZK] Is it a timepiece of any kind? No

I can't think of anyone who has a piano except in Jane Austen novels so I don't know why I'm asking!

Did Jane Fairfax have a piano?

You have definitely got the right person (having checked all the imdb clues). And I am guessing that the piano is right as well.

ZK - YES!!! Congratulations! I'd thought after the last round of answers that someone must get it soon. The colour clue is that everyone thought that the piano was a gift to Jane Fairfax from the Dixons, which leads by association to Dixon of Dock Green, which Ania Marson, who played Jane Fairfax in the first TV version of Emma, appeared in a number of times. I did say it wasn't so much a clue as a lateral association which wouldn't help...
I'll shut up now and hand over the baton to ZK.