This is the 10 daler plate (think this one's in the Stockholm museum).
As far as I understand it, these were mostly used as shipping ballast to exchange for goods at the proposed destination (or wherever the copper price was best), although the lower denominations did circulate.
Much of the Swedish plate in the market today (about 3000 pieces) was recovered from the wreck of the Nicobar in 1987.
I don't know where mine came from, but it's almost certainly marine salvage judging by the condition. Still weighs in at 237.5g though.