Diamond slab saw, most likely your best bet cutting it up. Take it to a local rock club to see if its jade, but there is another test you can do. It's not a "perfect-positive" test, but it's worked for many of the pieces of jade I have. Take a hair, hold it very tightly around one of the corners and move a flame across it where it touches the rock. Jade dissipates heat very quickly and most times the flame will not burn the hair, even if left on the hair for a second or two. But the best bet is to have it looked at by someone who is educated and equipped to make a determination on physical/optical properties. I hesitate to even guess, but without a better, bigger picture, my first instinct is telling me it's jasper.