That thing is fine, to me. Imagine that it's been, most likely, buried for over 2000 years? Very good, my friend.
Green crusty stuff is probably copper salts with the copper coming from impurities in the silver. There are chemicals that could remove it, but the coin is nice the way it is. Thanks for posting. Cal
Yes, some of the debased silver later Roman coins can acquire very colorful patinas due to their very high copper content. Cornelia Salonina, BI antoninianus, 260-268 AD. Obverse: SALONINA AVG Bust of Salonina, diademed, draped, right, on crescent. Reverse: FECVNDITAS AVG Fecunditas, draped, standing left, holding cornucopiae in left hand; at her feet, child; delta right. Rome Mint RIC 5 (Gallienus), MIR 36, 581aa; RSC 39a 2.43 grams
