Definitely you can cut them to usable pieces ... now it's a double win. New full size, and the smaller ones will be handy for other reasons. If you have smaller pieces than you mentioned, cut them into usable squares/rectangles too. I can't believe how often I use my little 2-1/2" square. Perfect when I want something FC!
Not sure what a dremel is? ... but yes, basically it cuts the same as glass.