sedimentary

Chalcedony or chert pebble with iron-oxide staining

Microcrystalline quartz (SiO₂), possibly a weathered chert or flint nodule

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; gray-brown, dull to waxy luster, very fine-grained and conchoidally fracturing. The pale outer rind and darker interior suggest weathering and iron/mineral staining; no visible cleavage.

Identified August 16, 2026More sedimentary →

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At a glance

Common name: Chalcedony or chert pebble with iron-oxide staining
Scientific name: Microcrystalline quartz (SiO₂), possibly a weathered chert or flint nodule
Category: sedimentary
Identified: August 16, 2026
Method: Standard

AI Estimated Value

Typically $1–$10 as a common pebble; approximately $10–$30 if it proves to be a distinctive silicified fossil or attractive polished specimen.

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

Likely formed when silica-rich groundwater replaced or cemented sediment, producing microcrystalline quartz; the outer cortex developed during weathering. Exact geological age cannot be determined from the photograph.

Uses & applications

Used historically for cutting tools and fire-starting, and today as a lapidary or collecting material; generally not valuable as construction stone.

Geological facts

Chert and chalcedony are varieties of microcrystalline quartz, often difficult to distinguish visually without testing. The dark center may also represent a silicified fossil or another included mineral.

Field identification & locations

Common in river gravels, limestone terrains, and weathered sedimentary formations. Test with a steel file or glass: genuine quartz-rich chert can scratch glass; a freshly broken surface should be smooth and waxy rather than granular.