by The Earth (as told to Amy)
1. Create a cavity deep within an existing rock. You can do this 2 different ways: either by trapping a pocket of gas (or water) in cooling lava, or – if you’re so inclined- bury something inside a rock that will decay (wood, coral or dissolvable minerals) and leave you with the cavity you require. Think of it as a mini-cave, and a cave as sometimes a giant geode.
2. Choose which kind of crystal will form inside the cavity by adjusting the location, temperature, acidity, and the type of surrounding rock.
3. Now send mineral-rich water (groundwater or rainwater, up to you!) to suffuse the tiny pores in the growing rock shell and fill the cavity.
4. Take the minerals out of the water and line the cavity with them. Evaporate the water. Repeat this consistently for thousands of years. If you are building a particularly big geode, you can expect to spend nearly a million years in the making of it. Over time, this mineral-lining will form the crystals inside the geode.
Since geodes take time and are built from the outer rim in, the outside of the stone will be much much older than the inside. Some of my favorite geode projects I have done include:
