The stone antiquarians treat so cryptically (7)
I believe the answer is:
rosetta
'the stone' is the definition.
(I've seen this before)
'treat so cryptically' is the wordplay.
'cryptically' is an anagram indicator.
'treat'+'so'='treatso'
'treatso' is an anagram of 'ROSETTA'.
'antiquarians' acts as a link.
I am not very happy about this link. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for rosetta that I've seen before include "Whence Champollion's stone" , "The - Stone helped read Egyptian hieroglyphics" , "Inscribed basalt slab (found 1799), key to deciphering Egyptian hieroglyphs" , "Source of revelatory stone" , "Place stone key to Egyptian studies was found" .)