HOW MEXICAN GEODES FORM

CONDENSED VERSION

STEP 1: The spheres that become beautiful geodes begin as bubbles formed in lava flow.

STEP 2: The bubble is cast in a hard shell of silica and water containing dissolved minerals is trapped inside.

STEP 3: The precipitate can contain a wide variety of minerals, usually quartz or calcite, but also aragonite, magnetite, barite and chalcopyrite.

STEP 4: The precipitate forms a lining of inward projecting crystals and since different minerals harden at varying temperatures, the material forms layers, which result in beautiful outer banding and inner crystalline structure.

Sometimes a cavity may be completely filled by layers, which is referred to as “nodules”

STEP 5: Over thousands of years, weathering lifts the, now formed geode, from the surrounding rock.

Mexican geodes are literally hand dug out of tough bentonite clay with a pick axe.

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