sedimentary
Chert with Druzy Quartz and Mossy/Iron Inclusions
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs), Color: Grey, tan, and white with yellow/orange moss-like iron inclusions, Luster: Dull to waxy with sparkly druzy crystals, Structure: Microcrystalline with small surface pockets
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Physical properties
Hardness: 7 (Mohs), Color: Grey, tan, and white with yellow/orange moss-like iron inclusions, Luster: Dull to waxy with sparkly druzy crystals, Structure: Microcrystalline with small surface pockets
Formation & geological history
Formed through the replacement of limestone by silica-rich fluids or precipitation from water in sedimentary basins. These specimens often originate from Paleozoic era deposits.
Uses & applications
Used historically for stone tools and flints; currently valued by collectors for lapidary work, cabochons, and as rough landscape specimens.
Geological facts
Chert is one of the most durable rocks and has been used by humans for millions of years. The yellow hair-like growth visible is likely limonite or iron oxide staining on fibrous mineral growth within the pockets.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and conchoidal fracture. Common in limestone outcrops. Look for the sparkle of micro-quartz crystals in the rough crevices.
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