How geodes are formed?

PEOPLE are crazy for geodes right now. A geode may look like a plain, ugly rock from the outside, but when it is broken open, it is filled with beautiful crystals. People use the crystals for decoration and jewellery. But where do they come from? Geodes are born when a cavity develops in a rock. These holes are often formed by lava cooling around a gas bubble. When the gas escapes, it leaves a pocket of space in the volcanic rock shell. Then mineral-rich water seeps through tiny pores in the shells. The water evaporates, leaving the minerals behind. Over thousands of years beautiful crystals are form. They are
all gorgeous!