Bicentennial quarter seems to be silver, no mint mark, weight 5.78g Edge of coin…

If your balance is accurate, it suggests silver. But it could easily be off. Look at the edge: if you see copper sandwiched between, it's copper-nickel; if not, silver. Since it's Philadelphia (no mint mark), it's not a proof. But without an "S" mint mark, I have to say it's not silver. The color is more copper-like as well. So your coin isn't worth a whole lot more than a quarter, if uncirculated it has a retail value of about a dollar. Hope that helps.