Igneous Rock

If your rock is extremely dark, it is most likely Basalt. It was formed by quickly cooled lava.

If you have a black and white rock where you can clearly see the minerals inside, you have Diorite or Gabbro. Gabbro is the darker rocks above. Diorite has more of the white minerals (quartz and plagioclase feldspar)

If your sample has any pink in it, then you have Granite! The pink is Potassium Feldspar. It is formed by slow cooling of magma deep within the earths surface.