Lenin,
First off, thanks for posting. Next, what is the approximate century of other material coming from this area? Your cob which is indeed a little off in weight but then again it looks quite worn which may explain this...but as Mack says it is "light in weight"
Let's just say its worn...what I think you have is a Potosi 1 real (cob) and looks to me like assayer T over R which puts date about late 1630s to about 1648 (Practical Book of Cobs)
I will post a photo which resembles your find...compare and then you all can decide.
I will stick to my ID till other wise.
Trez
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