If your rock resists nails and vinegar, then you have Quartzite!
Quartzite could have been formed by Chert or Sandstone, and has lots of the mineral Quartz inside!
If your rock can be scratched with a nail and fizzes when vinegar is put on it, then you have Marble!
Marble is used for decoration.
If you identified one of the above rocks, please enter it into the survey below: