Despite its worn condition, I couldn't resist to buy this silver Tetradrachm at a very affordable price.Obverse shows Otacilia Severa head Left. Reverse has an eagle head right. Antiochia SC in exergue. It weighs only 8.66 g. Prieur390. I wonder if this coin is a tridrachm or what. Never seen a silver Tet of this weight !
How much mass is missing? You would be surprised with coins with severe environmental corrosion how much mass they can lose. This one might have lost silver inside as well being buried 1800 years. Random coin finds can have this happen. The best ancients are found in pots protected from ground water.
The coin is a tetradrachm in name only. There will not be much silver in it. It's just a debased coin and normal for the type.
7Calbrey, Your Tet of Otacilia Severa has a great deal of corrosion which accounts for the light weight. The weight standard at that time was about 12.00 gm for that type, so my example pictured below would be considered heavy. David is right, the standard silver content for these coins was about 16.5%, & your coin looks even less than that if the photo color is accurate . If it's any comfort, your coin is listed as McAlee 1093 & considered (V. Rare) !
I have a similar situation with an Alexandrian tet of Galba, weighing around 7.5 grams instead of 12. As you can see, there is corrosion with the coin which has eroded the silver content (and maybe the base metal).
