sedimentary
Thunder Egg (Agate/Jasper filled)
Chalcedony variety Agate/Jasper in a Rhyolitic matrix
Hardness: 6.5-7 (Mohs scale); Color: Brown, yellow, ochre, transluscent grey; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None
- Hardness
- 6
- Color
- Brown, yellow, ochre, transluscent grey
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Brown, yellow, ochre, transluscent grey; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None
Formation & geological history
Formed within gas bubbles in rhyolitic volcanic ash layers where silica-rich groundwater deposited minerals over millions of years, typically during the Eocene epoch.
Uses & applications
Commonly used for lapidary work, jewelry making, bookends, and as a popular collector's specimen due to its unique internal patterns.
Geological facts
Thunder eggs are the state rock of Oregon. According to Native American legend, they were stones thrown by the spirits of Mount Hood and Mount Jefferson during thunderstorms.
Field identification & locations
Identified by a rough, drab exterior that hides a colorful, star-shaped or solid core of agate or jasper when sliced. Often found in specific beds within volcanic tuff.
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