sedimentary
Botiroidal Chalcedony or Silicified Fossil Coral
Silicon Dioxide (SiO2) - Chalcedony / Scleractinia (if fossilized)
Hardness: 6.5-7 (Mohs scale), Color: Creamy white to pale tan, Luster: Waxy to vitreous, Structure: Botryoidal (grape-like) or mammillary, Cleavage: None
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: Creamy white to pale tan, Luster: Waxy to vitreous, Structure: Botryoidal (grape-like) or mammillary, Cleavage: None
Formation & geological history
Formed by the precipitation of silica-rich fluids in cavities within sedimentary or volcanic rocks. The distinctive dimpled surface suggests either botryoidal growth or the silicification of a colonial coral structure, likely occurring during the Cenozoic or Mesozoic eras.
Uses & applications
Primarily used as a collector specimen, for lapidary work (cabbing or carving), or as decorative landscaping stone.
Geological facts
The 'eyes' or dimples on the surface are characteristic of chalcedony replacing organic structures or forming in bubbly clusters. If it is high-quality limb cast or coral fossil, it is highly prized by rockhounds.
Field identification & locations
Identify by its waxy texture, hardness (cannot be scratched by a steel knife), and repetitive rounded surface patterns. Commonly found in riverbeds, silica-rich volcanic ash beds, or limestone regions like Florida or the Western US.
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