Largest Geode in the World: Crystal Cave and Pulpí

The largest geode in the world is Crystal Cave, under Heineman's Winery at Put-in-Bay on South Bass Island, Ohio — a cavity big enough to walk into, lined with pale blue tabular crystals of celestine, the strontium sulfate mineral also spelled celestite.

Gustav Heineman, who had emigrated from Germany in 1887, was digging a well beneath his winery in 1897 when he broke into it at 30 feet down. The crystals on its walls run from 8 to 18 inches, with some reaching about three feet across.

For a while the cave was a mine rather than a sight: celestine was extracted from it for the manufacture of red fireworks, since strontium is what gives fireworks their red colour. Heineman eventually stopped mining and opened it to visitors, and the ticket income helped the winery survive Prohibition. It is still open seasonally today.

The most spectacular geode found in modern times sits inside the abandoned Mina Rica mine in the Sierra del Aguilón at Pulpí, Almería, in southeastern Spain. It is an ovoid cavity about 11 metres long, and its walls are covered in gypsum crystals up to two metres in size, so transparent that researchers compared them to ice.

A team led by Juan Manuel García-Ruiz published the explanation in the journal Geology in 2019. The crystals grew at around 20 °C — not in a hot hydrothermal system — at a shallow depth where surface temperature swings still reached the cavity. Because those swings stayed below the temperature of maximum gypsum solubility, around 40 °C, the crystals repeatedly dissolved a little and regrew, a slow coarsening process known as Ostwald maturation, while dissolving anhydrite supplied a steady stream of raw material.

The team also bracketed the age: the crystals formed after the Mediterranean dried out 5.6 million years ago, are probably younger than 2 million years, and are older than 60,000 years based on a carbonate crust coating one of them. The mine has been adapted for guided visits.

The Empress of Uruguay is the largest amethyst geode on public display. It stands 3.27 m tall and weighs about 2.5 tonnes in its present state, open along its length so visitors can see the purple crystal lining.

It was found in 2007 near the city of Artigas in northern Uruguay by the mining company Le Stage Minerals, and freeing it from the surrounding basalt took three months. It now stands at The Crystal Caves museum in Atherton, Queensland, Australia. Its top was cut and the uppermost crystals were sold separately, while the rest was kept intact for exhibition. The owners value it at about US$190,000 and it is not for sale.

A cautionary footnote for anyone displaying a large specimen: in 2011 a visitor secretly broke off a piece roughly the size of a tennis ball.

Three different things are being measured when people argue about the biggest geode, which is why the answer changes depending on who is asking.

• Cavity size. Crystal Cave wins here: a walk-in cavity found 30 feet below a winery floor.
• Crystal size. Pulpí wins, with transparent gypsum crystals up to two metres. Its cavity is roughly 11 metres long, far smaller than a cave but enormous for a geode.
• Specimen size. The Empress of Uruguay wins among geodes that were removed whole and put on display, at 3.27 m and 2.5 tonnes.

There is also a boundary problem. A geode is defined by an original cavity lined with inward-growing crystals, and a limestone cave is defined by dissolution. Crystal Cave is called a geode because it is a mineral-lined cavity in the rock rather than an ordinary solution cave, but the biggest examples of anything tend to sit near the edge of the definition.

All three are open to visitors, which is unusual for record-holding geological sites.

Crystal Cave, Put-in-Bay, Ohio. Open seasonally from early May through late September, seven days a week, with tours priced at US$8 for adults and US$4 for children aged 6 to 11 as listed on the operator's page in September 2026. Reaching South Bass Island means a ferry.

The Geode of Pulpí, Almería, Spain. The mine has been adapted for visits; expect a guided route inside a former mine, which means fixed group times.

The Empress of Uruguay, Atherton, Queensland. Displayed indoors at The Crystal Caves museum, roughly an hour and a half inland from Cairns.

Check opening times and prices with each site before travelling, since all three are small operations with seasonal hours.

The largest crystals ever found are not in a geode but in the Cave of the Crystals at Naica, Chihuahua, Mexico, found in April 2000 by the brothers Juan and Pedro Sánchez while drilling for the mining company Industrias Peñoles. According to Wikipedia, the biggest selenite (gypsum) crystal there is 11.4 m long, about 5 cubic metres in volume, with an estimated mass of 12 tonnes.

The cave lies 300 m below the surface, reached up to 58 °C with 90 to 99% humidity when drained, and an unprotected person could survive only about ten minutes inside. Mining stopped and the cave was allowed to re-flood in October 2015, so it cannot be visited.

Check which source a number comes from before repeating it:

• Crystal Cave discovery year. The operator's page and World Record Academy give 1897; Wikipedia and FossilEra give 1887, the year the operator's history gives for Gustav Heineman's emigration from Germany.
• Crystal Cave size and depth. FossilEra gives about 30 feet long; World Record Academy gives 35 feet long and 35 feet below the surface.
• Pulpí. Wikipedia gives 8.0 by 1.8 by 1.7 m and a discovery in 1999; FossilEra gives 26 by 6 by 5.5 feet, about 11 cubic metres, found by the Mineralogist Group of Madrid, with public tours from August 2019.
• Amethyst by weight. FossilEra lists a Guinness-recorded amethyst geode of 13,090 kg at the Shandong Tianyu Museum in China, and the Enchanted Cave at Byron Bay, Australia at over 20,000 kg and 18 feet wide. The Empress of Uruguay, above, is the tallest on display rather than the heaviest.

Giant geodes do trade. Dealer asking prices on FossilEra, checked 2026-09-25:

• Amethyst geode section with calcite, Uruguay, 21 in: US$1,950
• Deep purple amethyst geode on a stand, 49.5 in: US$22,500
• Giant quartz geode display, 50 in: US$22,500
• Egg-shaped amethyst geode on a metal stand, 48 in: US$26,100

Record pieces are a different market: the owners of the Empress of Uruguay value it at about US$190,000, as noted above, and it is not for sale.