If you give me the date and look on the reverse of the coin at the bottom center and see if it has a mintmark I can tell you. Tarnished is fine, even dark tarnish, silver tarnishes over time, as stated never clean the tarnish off a coin, if you do it will ruin the value and then be worth face value.
Many a good coin has been ruined by the person cleaning the coin to make it look better, not knowing the consequences, then when they go to sell and they find out it has no value, just scrap value, or face value. BP