Appreciative, having this much coal? (8)
I believe the answer is:
grateful
'appreciative' is the definition.
('grateful' can be similar in meaning to 'appreciative')
I cannot understand how the rest of the clue works.
(Other definitions for grateful that I've seen before include "Beholden" , "Thankful, appreciative" , "Showing thankfulness" , "Showing gratitude" , "Showing appreciation for kindness" .)