How to Buy Geodes

Pick up several different geodes, comparing their weights and choosing the lightest one.

Continue comparing weights, setting aside any that feel somewhat light for their size until you've set aside about a dozen lighter geodes.

Weigh the small pile of geodes you have set aside, eliminating the ones that are heaviest for their size.

Inspect the remaining geodes for size and shape, eliminating any that are not the size you are looking for or that are not an eye-pleasing shape. They do not necessarily need to be perfectly round, but if you dislike the shape, eliminate that geode.

Set aside geodes that are extraordinarily light for their size.

Inspect the light geodes for signs that they may contain mud rather than crystals. Although there are not always obvious signs, mudballs will often have brown or black streaks on the exterior and may have pieces of the exterior chipped away, revealing an ugly brown interior. Eliminate any geodes that are likely to be mudballs.

Examine the exteriors of the remaining geodes. If the exterior is completely white, without a blue or black undertone, the geode is likely to contain white quartz crystals or light-colored banded agate. If it has black, blue or purple undertones, it may contain amethyst or other colored quartz crystals or blue banded agate. Keep the geodes with exteriors that match what you hope to find inside.

Check the exterior for any chips or cracks that reveal the interior. Although it's not common, some geodes will have small openings that will reveal their inner contents. If you see a hole or crack that reveals something you like, hang on to that geode.

Weigh the remaining geodes, choosing the ones that are lightest.