sedimentary
Dendritic Agate or Moss Agate Nodules (Septarian-like)
Chalcedony with mineral inclusions (SiO2)
Hardness: 6.5-7 Mohs. Color: Green, brown, tan, and cream. Luster: Waxy to vitreous. Crystal structure: Trigonal (microcrystalline). Opaque to translucent with concentric and dendritic patterns.
- Hardness
- 6
- Color
- Green, brown, tan, and cream
- Luster
- Waxy to vitreous
Identified More sedimentary →
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Physical properties
Hardness: 6.5-7 Mohs. Color: Green, brown, tan, and cream. Luster: Waxy to vitreous. Crystal structure: Trigonal (microcrystalline). Opaque to translucent with concentric and dendritic patterns.
Formation & geological history
Formed within cavities in volcanic or sedimentary rocks where silica-rich fluids deposit layers of chalcedony. The green patterns are typically caused by oxides of manganese or iron forming moss-like inclusions.
Uses & applications
Primarily used for ornamental purposes, lapidary art, jewelry, and as display specimens for collectors.
Geological facts
While identifying specifically as an agate, such circular cut specimens often mimic the appearance of septarian nodules or thundereggs when polished into rounds. Agate has been used by humans for over 3,000 years for seals and talismans.
Field identification & locations
Identified by its waxy luster, variety of colors in concentric zones, and extreme hardness. Common in Brazil, India, and the United States. Look for circular patterns and a lack of visible crystal grains.
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