sedimentary
Rough Chalcedony / Jasper Agate Nodule
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness 6.5-7 on Mohs scale; color ranges from reddish-brown, tan, to gray with translucent quartz pockets; dull to waxy luster; conchoidal fracture; hexagonal microcrystalline structure; specific gravity ~2.6.
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Physical properties
Hardness 6.5-7 on Mohs scale; color ranges from reddish-brown, tan, to gray with translucent quartz pockets; dull to waxy luster; conchoidal fracture; hexagonal microcrystalline structure; specific gravity ~2.6.
Formation & geological history
Formed through silica precipitation from fluids filling cavities or replacing organic materials in sedimentary host rocks or weathered volcanic beds. Common in ancient river gravels and silica-rich weathering environments.
Uses & applications
Used primarily by lapidaries for tumbling, slabbing, cabochon cutting, and decorative stone carving. Also popular among rockhounds and mineral collectors.
Geological facts
Raw silica nodules like this often hide vibrant banding, fortification patterns, or mossy inclusions inside that are only revealed when sliced and polished.
Field identification & locations
Look for a combination of waxy luster on fractured edges, high hardness (scratches steel), and translucent microcrystalline quartz regions. Found frequently in riverbeds, desert pavements, and gravel pits.
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