sedimentary

Iron-stained chert or chalcedony nodule

Microcrystalline quartz (SiO₂), likely chert with chalcedonic silica and iron-oxide staining

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; brown, tan, and rusty yellow with dull to waxy luster. Massive, cryptocrystalline quartz, lacking visible cleavage; the pale interior appears conchoidal or smoothly fractured.

Identified August 14, 2026More sedimentary →

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At a glance

Common name: Iron-stained chert or chalcedony nodule
Scientific name: Microcrystalline quartz (SiO₂), likely chert with chalcedonic silica and iron-oxide staining
Category: sedimentary
Identified: August 14, 2026
Method: Standard

AI Estimated Value

Typically $2–$15 for a common rough specimen; approximately $20–$75 if unusually attractive, polished, or demonstrably from a notable locality.

Not an official valuation

AI estimate for general interest only — not an appraisal. Actual value depends on condition, provenance, and market demand. Verify with a professional before buying, selling, or insuring.

This identification was generated by AI and may contain errors. Verify important details before relying on them — and never use an AI result to judge whether a specimen is safe to handle. Read the full disclaimer

Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities or replaces carbonate and other sediments, commonly producing nodules; iron oxides create the orange-brown staining. Exact geological age cannot be determined from the image and depends on its host formation.

Uses & applications

Used as a durable aggregate, road material, flint-like toolstone, and lapidary rough; attractive pieces may be polished for display, though this specimen appears largely ordinary.

Geological facts

Chert and chalcedony are chemically similar but differ mainly in texture and microstructure. A fresh broken surface should be glassy and may show conchoidal fracture.

Field identification & locations

Common in limestone, chalk, and other sedimentary terrains worldwide. It can scratch ordinary glass, shows no fizz with dilute hydrochloric acid unless carbonate is present, and is much harder than surrounding clay or limestone.