Are silver quarters still in circulation?

Not a real one.

Lots of private companies have taken ordinary copper-nickel State Quarters, plated them with a thin layer of gold, and sold them at large markups as "collectibles". However there's almost no secondary market for them so they're really only worth face value. Sometimes people spend them when they realize they're not going to make anything on their "special" collection.

If you think about it for a second or two, a genuine gold quarter would be worth hundreds of dollars. Even the most foolish government bureaucrat wouldn't authorize making a coin that lost the Mint hundreds on each one they made.