Hard mineral perhaps I ordered (8)
I believe the answer is:
sapphire
'hard mineral' is the definition.
The answer and definition can be both substances as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'perhaps i ordered' is the wordplay.
'ordered' indicates an anagram.
'perhaps'+'i'='perhapsi'
'perhapsi' is an anagram of 'SAPPHIRE'.
Can you help me to learn more?
(Other definitions for sapphire that I've seen before include "His paper can be made into a jewel" , "Blue gemstone" , "precious item" , "Deep blue - precious stone" , "Birthstone for September" .)