I guess lamination? ROMAN IMPERIAL, Septimius Severus Denomination: AR denarius, minted: Laodicea ad Mare; 194 AD Obv: L SEPT SEV PERT AVG IMP II: Head of Septimius Severus, laureate, right Rev: MONETA AVG: Moneta, draped, standing left, holding scales in extended right hand and cornucopiae in left hand Weight: 2.21g; Ø:1.8mm Catalogue: RIC IV 460a Provenance: Ex priv col; acq.: 12-2018
It looks like there was lamination within the silver and at some point the coin has been subjected ot an impact, causing a crack and a separation of a lamination layer. That would be my guess.
I agree with Maridvnvm on the lamination but the obverse is IMP CAE L SEP SEV PERT COS II and the style is standard mid-194 'Emesa'. As time progressed at this mint, the portraits changed from long and slender to rounder. Metal quality varied. I would not be surprised to find they used many sources of metal including recycling older coins melted with a few overstruck. We see quite a variation on metal quality.
