Thanks and yes, JAZ Numismatics! That's my go-to guy! I have another too share... Caracalla, AD 198-217 AR denarius, 3.01g, 20mm, 6h; Rome mint, AD 210-213. Obv.: ANTONINVS PIVS AVG BRIT; laureate head right. Rev.: MONETA AVG; Moneta standing left, holding scales and cornucopia.
I found another two low weight denarius in my collection: Elagabalus (about 1.6gr) and Julia Mamaea (1.8 gr).
I'll try to photograph Caracalla with digital microscope, but I'm still not handy with a photographing coins. These pictures are made with mobile phone.
Nothing suspicious about the new photos. Here's my favorite Caracalla because he looks like a real thug in the portrait.
Leeching would be my conclusion. My lightest Severan denarius was 1.459 gms and certainly seemed to have suffered from leeching where the copper was chemically extracted by the deposit conditions around it.