Black mineral providing the exterior for a great hall (8)
I believe the answer is:
basilica
'great hall' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'black mineral providing the exterior for a' is the wordplay.
I cannot really see how this works, but
'black' could be 'b' (abbreviation as in pencil hardness) and 'b' is found within the answer.
'mineral' could be 'silica' (silica is a kind of mineral) and 'silica' is found within the answer.
'a' is within the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for basilica that I've seen before include "Roman-style church" , "Roman building used for public administration" , "Large (Roman Catholic) church" , "Important church, like St Peter's in Rome" , "Church or cathedral of high rank" .)