Almost certainly Argyle but no audit trail. A buyer should send it for 3rd party origin report. The very strong deep colour is good, but the slightly brownish colour is a negative.
I am told and believe it to be recut from an Argyle diamond. There is no inscription but if there is a serious buyer I will chase down any available documentation. It can also go to a 3rd party lab for an origin report.
Seen as stone #15 with previous owner. Is still excellent value. Said to be Argyle, pre inscription, or inscription removed. Exceptional colour but unusual shape.