|Chinese Sycee coin.
This is, almost certainly, a fake. For about a thousand years ending in the early 20th century, stamped silver ingots like this were used as currency: I'm told one like this would have fed a family for a month. But in the 1930s there was a mandatory melting down program to turn all the old currency into new currency, so very few genuine Sycee coins remain, and they are valuable antiques.
Because they are valuable, they are often counterfeited, sometimes in quite sophisticated and difficult to detect ways. For example, a latex mold can be made of a real one, and castings made from that mold, in real silver. These can be very difficult to distinguish from the genuine article.
In this case, however, I paid less than 1/5 of the melt-down value of this coin, which weighs about 1300 grams. It's pretty unlikely that anyone would sell something actually made of silver for less than the value of the silver. So it's almost certainly not silver and therefore not genuine.
The interesting question is whether it's a new forgery or an old one. Turns out fake ones were made in great numbers while these coins were in circulation, and the government did not destroy those, only the real ones. So there are a large number of old fakes being sold. Of course, being old and with a story, the fakes are now valuable antiques too, if they are in fact old. (New fakes won't be valuable for another hundred years or so.)
I have no idea whether this is a new or an old fake. It looked old before I cleaned it (of course, I only cleaned it after I was pretty sure it wasn't real, because polishing a genuine silver Sycee would probably not be a good idea from a historical preservation point of view). I will, however, soon know whether it's got real silver in it: I'll have it tested as soon as I have a free afternoon.
In the mean time, here are some interesting sites about this type of coin:
And in case you can read Chinese, here is the inscription from the bottom and the characters drawn cleanly by my colleague Xin Kai from Singapore:
Source: eBay seller chinaembroidery
Contributor: Theodore Gray
Acquired: 3 June, 2003
Text Updated: 29 January, 2009
Sample Group: Coins