mineral

Quartz Geode

Silicon Dioxide (SiO2) in Calcareous or Siliceous Matrix

AI-generated identification · may be incorrect

Hardness: 7 (inner quartz); Color: Tan/white exterior with clear to white crystalline interior; Luster: Vitreous (internal), Dull (external); Structure: Hexagonal crystals inside a spherical nodule; Specific Gravity: 2.65.

Hardness: 7 (inner quartz)
Color: Tan/white exterior with clear to white crystalline interior
Luster: Vitreous (internal), Dull (external)

Identified July 21, 2026More mineral →

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Physical properties

Formation & geological history

Formed as hollow cavities in sedimentary or volcanic rock. Over millions of years, mineral-rich groundwater seeps into the cavity, depositing layers of silica or calcite crystals. This specimen appears to be of the sedimentary variety, likely from the Mississippian or Ordovician period.

Uses & applications

Primary use is for educational display, home decor, and mineral collecting. Large, high-quality geodes are sometimes sliced and used for jewelry or high-end interior design elements.

Geological facts

Geodes are essentially 'pocket' rocks. You can never perfectly predict what is inside until they are cracked open or sawed. The Keokuk geodes from the Midwestern US are some of the most famous examples globally.

Field identification & locations

Identify in the field by looking for rounded, lumpy nodules that feel lighter than they look (indicating a hollow center). Common in limestone or volcanic ash beds. Look for white crystalline patches on the surface where the shell has chipped.