The three-meter tall amethyst geode - a hollow rock filled with amethyst crystals - is the main attraction at the Crystal Caves at Atherton, southwest of Cairns. But it's now missing a bit after a ...

Slowly, these minerals crystallize, forming a dense lining of quartz or other silicates that can include a variety of crystals like amethyst, calcite or celestite. When a geode splits open ...