Yellow aggregate containing clay and hematite primarily (5)
I believe the answer is:
ochre
'yellow' is the definition.
(ochre is a kind of yellow)
'aggregate containing clay and hematite primarily' is the wordplay.
'aggregate' becomes 'ore' (I've seen this before).
'containing' indicates putting letters inside.
'clay' becomes 'c' (this might be a standard abbreviation which I don't know about).
'and' is a charade indicator (letters next to each other).
'primarily' suggests taking the first letters.
The initial letter of 'hematite' is 'h'.
'c'+'h'='ch'
'ore' going around 'ch' is 'OCHRE'.
Can you help me to learn more?
(Other definitions for ochre that I've seen before include "Orange" , "Mineral pigment; chore (anag.)" , "natural colouring" , "Chore using pale brownish colour (5)" , "Pigment made from clay and iron oxide" .)