Fulgurites or "petrified lightning" form when lightning strikes sand and fuses it into glass. The glass is an impression of the form of the lightning bolt. Fulgurites occur naturally, but there are a couple of ways you can make fulgurites yourself.
Make a Fulgurite - Safe Method
Don't put yourself at risk of a lightning strike! The best way to make a fulgurite is to be safely indoors when it's stormy outside.
- Check the weather forecast to find out when lightning activity is expected. Radar is good or refer to special maps for your area that record lightning strikes. You must complete preparation for a fulgurite several hours (or longer) before the storm arrives.
- Drive a lightning rod or length of rebar into sand about 12 inches to 18 inches and extending up into the air. You can set up colored sand or some granular mineral besides quartz sand, if you prefer. There is no guarantee lightning will strike your lightning rod, but you improve your chances if you select an open area where the metal is higher than the surroundings. Choose an area far from people, animals or structures.
- When lightning approaches, be far away from your fulgurite project! Do not check on whether you make a fulgurite until several hours after the storm has passed.
- The rod and sand will be extremely hot after a lightning strike. Use care when checking for a fulgurite so that you don't burn yourself. Fulgurites are fragile, so dig around it to expose it before remove it from the surrounding sand. Rinse excess sand with running water.
You can go the Ben Franklin route making a fulgurite by drawing the lightning down to a bucket of sand. This method involves launching a D model rocket toward a thunderhead that is estimated to be due to discharge. A spool of thin copper wire connects the bucket to the rocket. While said to be quite successful, this method is extraordinarily dangerous because the lightning doesn't just follow the wire back to the bucket. It additionally follows the wire and the area around it back to the trigger used to launch the rocket... and you!
Simulated Lightning Fulgurites
A safer, though someone expensive method, is to use an xfmr or transformer to force man-made lightning
into silica or another oxide. This technique fuses the sand into lechatelierite, although it is much more difficult to achieve the branched effect seen in natural fulgurites.