These geodes are from Morocco, and form when fluids crystalize in rounded rock cavities. These contains abundance of sparkling crystals inside!
To break the geode:
It is a good idea to use safety goggles when breaking your geode. Use one of the following methods to :
You will need a hammer and a chisel. Take your hammer, cold chisel and geodes outside where there is a hard surface such as concrete walk, driveway, steps, etc. Place the geode on the concrete and hold it on the sides with one hand, then hold the cold chisel on the top of the geode and strike it LIGHTLY with your hammer. Don't try to break it open now.... Rotate the geode about a half inch, place the chisel in line with where you just hit it and strike the chisel again ... LIGHTLY. Do this all the way around the largest part of the geode. By the time you have hit the chisel in a line all the way around the geode, it should be ready to open. If the geode has not broken open at this point, start around the circumference again, striking the geode with the cold chisel in a straight line. Strike the chisel a little harder this time. This is a little slow method, but if you do it right and don't get in too big a hurry, you should be able to break the geode open into two halves that you can fit back together to where you can't tell where it was broken.
Alternatively, you can place the geode in an old sock or bag and carefully strike the geode repeatedly with the hammer until it breaks open, but, it most likely will end up in a few smaller pieces.