Were those issued by some private mint? I have never seen them. The term double eagle generally refers to 20 dollar US gold coins minted from the mid 1800s to 1933 (10 dollar gold pieces were known as just eagles).
Most modern bullion coins have been stamped to identify their silver content. If they don't say they are silver, you can clink them together and see if they make the sound of silver coins. If you bought them from a coin shop did they tell you they were silver?
Jim