These are neat-looking medallions made to look like old rouble coins from the reign of Nicholas I (1825 to 1855). They are not made out of silver, but of brass or base metal and, perhaps, silver plated. I've seen two different styles. Both have Nicholas on the front and the double headed Byzantine eagle on the back.
No genuine roubles were made with this pattern, so these are not really counterfeit coins. However, unsuspecting collectors may pay too much for one. It is always best to know the person you are buying collectibles from. Start small, and, if you are satisfied, continue building relationships with dealers you trust.
Approximate values for these pieces are:
worn: $5 US dollars approximate catalog value
average circulated: $10
well preserved: $15
fully uncirculated: $25