How geodes form
A geode is not a single mineral but a structure. It starts as a cavity: a gas bubble in lava, or a space left when a concretion dissolves in sedimentary rock. Mineral-rich water then seeps in over long periods and deposits crystals from the walls inward, usually quartz, sometimes amethyst, calcite, celestine or banded chalcedony.
The colour of a natural geode reflects what was in that water: colourless to white quartz, purple amethyst, pastel calcite or blue celestine. Many commercial geodes come from Brazil, Uruguay, Namibia and Mexico; the large amethyst geodes of Brazil and Uruguay come from the basalts of the Paraná traps.
Dyed and fake geodes
Two tricks are common enough to check every geode for.
- Dyed geodes: geodes are often dyed in bright, unnatural colours, electric blue, hot pink, neon green. Natural quartz geodes are white, grey, purple or earth-toned. If the colour pools in cracks or looks like ink, it is dye.
- Fake galena geodes: sold widely in Morocco, these are pottery shells lined with artificial points and painted black outside and white on the rim. A real geode's outer surface is rough natural rock, and its break shows rock, not fired clay.
- Glued halves: a geode sold as a matched pair should have two faces that fit exactly and a rim that continues across the break.
What a geode costs: price data from October 2026
Asking prices read on 28 October 2026. Size, crystal quality and whether the geode is natural or dyed explain most of the spread.
| Source | Listings | Price |
|---|---|---|
| eBay, Moroccan geodes, fixed price | 157 | Median $30, middle half $15 to $66 |
| eBay, highest listing | $785 |
How to judge and care for a geode
Look for a clean break, well-formed crystals that fill the cavity evenly, natural colour and an intact rim. Quartz geodes are hard (7 on the Mohs scale) and easy to look after: rinse in plain water and dry. Calcite-lined geodes are much softer and dissolve in acid; dust them only.
Questions collectors ask
Are Moroccan geodes real?
Many are natural quartz geodes. Watch for two fakes common in the market: geodes dyed in unnatural colours, and 'galena geodes' made from painted pottery.
How do geodes form?
Water rich in silica or other minerals seeps into a hollow in volcanic or sedimentary rock and deposits crystals on the walls over a very long time.
How much is a geode worth?
On 28 October 2026, fixed-price eBay listings for Moroccan geodes had a median asking price of $30, with the middle half between $15 and $66.