Guide
Every geode at a cracking shop started as a gas bubble in volcanic rock that slowly lined itself with crystals. From the outside they look like plain rocks; the shop's cracker is what turns them into two halves of something you want to keep. Here is what the common types look like inside, where they come from, and which cracker opens them. When you're ready, find a shop that will crack one for you.
Chihuahua, Mexico
The classic cracking geode and the one most shops run. Round, grey-white, and rough like a coconut, 2 to 7 inches across. Inside: clear or smoky quartz points, often with calcite, and sometimes a dark amethyst center or a glassy druzy lining. They crack cleanly along a natural seam, which is why they are the favorite for the Pirate Wheel and tabletop crackers.
Chihuahua, Mexico
A little rougher and more irregular than Las Choyas, with a thicker rind. The inside is usually a bright white quartz crystal lining, sometimes with calcite blades or agate banding near the wall. Sold as mostly hollow or semi hollow; the hollow ones give the dramatic cavity reveal.
Chihuahua, Mexico
Named for the fine, sparkling druzy quartz that coats the inside like frost. Smaller crystals than Trancas, but the sparkle under a light is the draw. Many fluoresce green under a black light because of the calcite, which is why several shops keep a UV flashlight by the cracker.
Chihuahua, Mexico
Semi hollow geodes with larger, well formed quartz points. Good when a customer wants a geode that looks like a mineral specimen rather than a cavity. Often with a thin agate band just inside the rind.
Chihuahua, Mexico
Dense, semi hollow geodes with a solid crystalline interior: a cross section of quartz rather than an open pocket. They take more force to crack, so shops usually run them in the large plier or hydraulic cracker, and the flat faces polish beautifully afterward.
Mexico and Brazil
A geode that still holds water sealed inside from when it formed. Hold it to a light and you can sometimes see the bubble move before it is cracked. Once opened the water is gone, so shops often let customers keep these whole or drill a window instead.
Atlas Mountains, Morocco
Thin walled, light, and mostly hollow, with a white quartz lining and sometimes a grey or bluish tint. They are inexpensive and easy to crack, which makes them the usual choice for kids and for break your own geode kits.
Mexico, Brazil, Uruguay
Geodes whose walls are banded agate: layers of blue, grey, white, or orange chalcedony around a quartz center. The banding shows best on a cut and polished face, so many shops crack them and then offer to polish the cut side.
Uruguay, Brazil, Mexico
Purple quartz. The extra large break open geodes with amethyst domes are a shop centerpiece; smaller Mexican geodes sometimes surprise with a purple center. Color ranges from pale lavender to deep grape.
Brazil
Small (1 to 3 inch) agate geodes with a grey banded rind and a druzy quartz center. Usually sold already split and polished, but whole mine run Oco geodes crack nicely in a tabletop ratchet.
Oregon, USA and worldwide
Not strictly a geode: a nodule that forms in volcanic ash with an agate or jasper center, often with a star shaped pattern. They are solid, so they are cut with a saw rather than cracked, and the polished face is the prize.
Utah, USA
Small, round geodes from Juab County, Utah, with a bumpy rind and a quartz or chalcedony interior, sometimes with a bluish tint. Popular with rockhounds who dig their own.
Iowa, Illinois, Missouri, USA
Classic American geodes from the Mississippi River area. Cauliflower textured outside, with quartz inside and sometimes calcite, pyrite, or kaolinite. Hollow ones crack well and are a staple at Midwest rock shops.
Usually just the price of the geode, which depends on size: a few dollars for a small Moroccan geode up to $50 to $250 for a large Las Choyas coconut. Most shops include cracking; a few charge a small fee for geodes you bring in.
Yes, with a hammer and chisel, a pipe cutter, or a sock and a hammer, but the results are messy and the geode often shatters. A shop cracker splits it along the seam so you get two clean halves.
Most often quartz: clear, smoky, or amethyst. Also calcite, agate banding, druzy sparkle, and sometimes water (enhydro). Nobody can tell for certain until it opens.
A 3 to 4 inch Las Choyas coconut geode. They are the most reliably hollow and crack cleanly.
See it happen: popular geode cracking videos from listed shops. Found something you can't place? Post it on the Geode ID board.