sedimentary
Geode
Quartz / Chalcedony nodule
Hardness: 7 on the Mohs scale. Color: Exterior is usually greyish-brown limestone, interior crystals vary widely (often clear to white quartz). Luster: Vitreous to dull. Crystal structure: Trigonal (quartz). Cleavage: None. Specific gravity: 2.65.
- Hardness
- 7 on the Mohs scale
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on the Mohs scale. Color: Exterior is usually greyish-brown limestone, interior crystals vary widely (often clear to white quartz). Luster: Vitreous to dull. Crystal structure: Trigonal (quartz). Cleavage: None. Specific gravity: 2.65.
Formation & geological history
Formed in hollow areas of sedimentary or igneous rocks, typically groundwater rich in silica and other minerals deposits minerals on the inner walls over millions of years.
Uses & applications
Used in lapidary arts, jewelry, decorative display pieces, and collected by rockhounds.
Geological facts
Geodes look entirely ordinary and rocky on the outside, but cracking or cutting them open reveals a sparkling hollow interior lined with crystal formations.
Field identification & locations
Found worldwide, particularly in limestone formations, deserts, and volcanic ash beds. Look for spherical, bumpy nodules that sound hollow or light for their size.
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