metamorphic

Rounded quartzite or quartz-rich sandstone cobble

Quartzite; predominantly microcrystalline quartz (SiO₂), possibly with minor iron-oxide staining

AI-generated identification · may be incorrect

Hardness about 7 Mohs; tan to gray-brown, dull to weakly vitreous luster, massive and non-cleaved, with a fine-grained texture. Its smooth, rounded shape results from natural abrasion; the image does not show diagnostic crystals.

Identified September 1, 2026More metamorphic →

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At a glance

Common name: Rounded quartzite or quartz-rich sandstone cobble
Scientific name: Quartzite; predominantly microcrystalline quartz (SiO₂), possibly with minor iron-oxide staining
Category: metamorphic
Identified: September 1, 2026
Method: Standard

AI Estimated Value

About $1–$10 for an ordinary cobble; $10–$50 if unusually attractive, provenance-specific, or suitable for lapidary work.

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 a weathered and stream-transported cobble derived from metamorphosed sandstone; quartzite commonly forms during regional metamorphism, typically from Precambrian through Phanerozoic rocks. A precise age and identification require a fresh broken surface or testing.

Uses & applications

Quartzite is used as aggregate, road stone, riprap, building stone, and occasionally countertops; attractive varieties are collected or cut for decorative objects.

Geological facts

Quartzite is generally tougher and more resistant to weathering than its sandstone precursor. Iron oxides can produce the brown or reddish coloration.

Field identification & locations

Look for a sugary quartz texture and grains that break across, rather than around, the original sandstone fabric; it should resist scratching by steel. Common in river gravels and glacial deposits worldwide.