sedimentary
Dendritic Agate (Blue Chalcedony)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Translucent grey to bluish-white with black/brown inclusions; Luster: Vitreous to waxy; Crystal Structure: Hexagonal (Cryptocrystalline); Cleavage: None/Conchoidal fracture.
- Hardness
- 6
- Color
- Translucent grey to bluish-white with black/brown inclusions
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Translucent grey to bluish-white with black/brown inclusions; Luster: Vitreous to waxy; Crystal Structure: Hexagonal (Cryptocrystalline); Cleavage: None/Conchoidal fracture.
Formation & geological history
Formed by the deposition of silica from groundwater in cavities of volcanic rocks or sedimentary formations. The dark patterns are manganese or iron oxide 'pseudo-fossils' that grew during mineral formation.
Uses & applications
Primarily used as a gemstone for jewelry (beads, cabochons), metaphysical healing practices, and as a collector's specimen.
Geological facts
Despite being called 'Dendritic Agate', it is technically a chalcedony because it lacks the concentric banding required to be a true agate. The 'dendrites' are not plant fossils but mineral growths.
Field identification & locations
Identify by its translucent waxy appearance and mossy or tree-like internal inclusions. Often found in riverbeds or gravel deposits in Brazil, India, and the United States (Montana).
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