A fine and rare bloodstone magical gem, Greco-Roman, 2nd-3rd century AD, the two-sided bloodstone

A fine and rare bloodstone magical gem, Greco-Roman, 2nd-3rd century AD, the two-sided bloodstone intaglio of oval outline, carved on one side to depict a crowned sun god bordered with Greek script, the other side depicting the cockerel-headed god Abrasax/Abraxas, with snake legs, holding a shield and whip his shield with an inscription, the background inscribed TAI TAI, to a later swivel mount on a half hoop ring, intaglio 1.7 x 1.4cm