mineral
Polished chalcedony (likely moss/ag ate)
Microcrystalline quartz, SiO₂; probable moss agate or jasper variety
AI-generated identification · may be incorrectHardness 6.5–7 Mohs; translucent cream, honey-yellow, gray, and brown coloration with cloudy or dendritic inclusions; waxy to vitreous luster, cryptocrystalline structure, and no visible cleavage. Rounded and glossy from polishing.
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Physical properties
Hardness 6.5–7 Mohs; translucent cream, honey-yellow, gray, and brown coloration with cloudy or dendritic inclusions; waxy to vitreous luster, cryptocrystalline structure, and no visible cleavage. Rounded and glossy from polishing.
Formation & geological history
Forms when silica-rich groundwater fills cavities and fractures in volcanic rocks, depositing chalcedony and iron/manganese-stained inclusions. Such agates commonly formed during the Cenozoic or older volcanic episodes, depending on locality.
Uses & applications
Used for cabochons, beads, carvings, ornaments, and inexpensive jewelry; attractive patterned pieces are popular among collectors.
Geological facts
Moss agate’s plant-like patterns are mineral inclusions rather than fossils or organic material. Yellow-brown tones commonly reflect iron oxides or hydroxides.
Field identification & locations
Identify by its waxy luster, translucency at thin edges, hardness, and conchoidal fracture; it should resist scratching by a steel knife. Common sources include Oregon, Montana, India, Brazil, Uruguay, and Madagascar.
