Coal: an ancient land imports it (10)
I believe the answer is:
anthracite
'coal' is the definition.
(anthracite coal is a kind of coal)
'an ancient land imports it' is the wordplay.
'ancient land' becomes 'thrace' (I've seen this before).
'imports' is an insertion indicator (inserted letters are imported).
'thrace' placed around 'it' is 'thracite'.
'an'+'thracite'='ANTHRACITE'
(Other definitions for anthracite that I've seen before include "kind of fuel" , "High-grade hard coal" , "Hard variety of coal" , "Hard type of coal" .)