Keokuk Geode — Quartz Crystal Interior, Ancient Seabed Formation, 501g — Field Find

THE FIND
A Keokuk geode, 501g — unassuming limestone exterior concealing a shimmering interior of natural quartz crystal formations. One of the most celebrated geode localities in the world, in a substantial specimen with real presence.

WHAT WE KNOW
Keokuk geodes are found in the tri-state region around Keokuk, Iowa — in the Warsaw Formation, a Mississippian-age limestone deposit laid down approximately 340 million years ago in a shallow inland sea. The geodes formed in nodules within the limestone, with silica-rich groundwater slowly depositing quartz crystals inward from the cavity walls over geological time. Keokuk geodes are specifically known for their variety of interior minerals — while most contain quartz or chalcedony, some also contain calcite, dolomite, pyrite, sphalerite, or barite. This specimen weighs 501g. The interior crystal development is visible in the photographs; please review for specific crystal type and formation detail.

THE STORY
The Keokuk geode field is one of the most productive and well-documented geode localities in North America — it has been collected since the 19th century and remains a benchmark for geode quality. The Warsaw Formation that produces them was once the floor of a warm, shallow sea covering much of the interior of North America. The geodes are the record of what happened in that seafloor after the sea retreated: groundwater moving through the limestone, depositing minerals in the cavities left behind by dissolved nodules, building crystal by crystal over millions of years.

WHY WE CHOSE IT
At 501g this is a substantial Keokuk geode — large enough to display as a centerpiece specimen rather than a shelf accent. The exterior gives nothing away, which is part of the point. Please review the photographs for interior crystal development and formation detail.

ABOUT THIS PIECE
Type: Keokuk geode (Warsaw Formation, Mississippian)
Origin: Keokuk region, Iowa/Illinois/Missouri tri-state area
Weight: 501g
Condition: Natural specimen — please review photographs for interior crystal development, exterior form, and natural variation.
Quantity: 1 — one of a kind.