sedimentary
Chalcedony Geode Fragment
Microcrystalline Quartz (SiO2) within a nodule
Hardness: 6.5-7 (Mohs scale); Color: Gray, black, and white; Luster: Dull outer, waxy or vitreous inner; Crystal Structure: Trigonal (microcrystalline); Cleavage: None, conchoidal fracture.
- Hardness
- 6
- Color
- Gray, black, and white
- Luster
- Dull outer, waxy or vitreous inner
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Gray, black, and white; Luster: Dull outer, waxy or vitreous inner; Crystal Structure: Trigonal (microcrystalline); Cleavage: None, conchoidal fracture.
Formation & geological history
Formed by the precipitation of silica-rich hydrothermal fluids or groundwater within cavities of volcanic or sedimentary rocks. The layered structure suggests rhythmic deposition over time.
Uses & applications
Used primarily as collector specimens, lapidary material for jewelry (cabochons), and as decorative ornaments.
Geological facts
Geodes are often called 'thunder eggs' when they are completely filled. This specimen is a fragment showing the hollow cavity where crystals or chalcedony layers grew inward.
Field identification & locations
Identify by the distinct contrast between the rough, rocky exterior and the smooth, often botryoidal or crystalline interior cavity. Found globally in volcanic ash beds or limestone regions.
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