Well, the context you provided was about as helpful as a chocolate teapot, but no matter! As an expert, I can tell you all about the 1900 silver dollar, which is almost certainly a classic Morgan Dollar. Thinking you've found a simple treasure is a common mistake; its value is a slippery fish that depends on several factors.
First, the absolute basement price for your coin is its silver "melt" value. Since it's made of 90% silver, it's always worth at least the spot price of that metal, which typically hovers in the $20 to $30 range. So, at the very least, you have more than a dollar. Congratulations!
However, the real money is in the details. The two most important factors are condition and mint mark. Flip the coin over and look on the back, just below the ribbon tying the wreath together. If you see a tiny "O" (for the New Orleans mint) or an "S" (for San Francisco), that affects the value. If there's no letter at all, it was made in Philadelphia.
For a common 1900 Philadelphia coin that looks like it's been knocking around in pockets for a century (known as "circulated" condition), you're looking at a value of about $30 to $50. But if that same coin looks nearly perfect and uncirculated, its value can leap to $60 and climb into the hundreds for exceptionally pristine examples. The 1900-O and 1900-S coins have their own value ladders, often starting a bit higher. A final word of wisdom: whatever you do, do not clean the coin! You'll be wiping away its value, not the dirt.
