igneous

Tumbled brown-and-black stone, likely basalt or andesite

Fine-grained mafic to intermediate volcanic rock; commonly plagioclase, pyroxene, and possibly olivine or iron oxides

AI-generated identification · may be incorrect

Dark gray-brown, mottled, and weakly lustrous with a fine-grained texture; estimated Mohs hardness 5–6.5, no visible cleavage, and likely specific gravity about 2.7–3.1.

Identified September 4, 2026More igneous →

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At a glance

Common name: Tumbled brown-and-black stone, likely basalt or andesite
Scientific name: Fine-grained mafic to intermediate volcanic rock; commonly plagioclase, pyroxene, and possibly olivine or iron oxides
Category: igneous
Identified: September 4, 2026
Method: Standard

AI Estimated Value

About $1–$10 as a common tumbled specimen; typically under $20 unless unusually attractive or sold as part of a curated collection.

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

Dark gray-brown, mottled, and weakly lustrous with a fine-grained texture; estimated Mohs hardness 5–6.5, no visible cleavage, and likely specific gravity about 2.7–3.1.

Formation & geological history

Likely formed from cooling lava, probably in the Cenozoic or older; subsequent weathering and tumbling produced the smooth rounded shape. Exact identification requires a fresh surface, streak, and mineralogical testing.

Uses & applications

Used as aggregate, road stone, landscaping material, and occasionally as a decorative tumbled stone; usually has little jewelry value.

Geological facts

The rusty brown areas likely reflect oxidation of iron-bearing minerals. Basalt and andesite can look similar in hand-sized, polished specimens.

Field identification & locations

Common in volcanic regions worldwide, including oceanic islands, western North America, Iceland, India, and Japan. A magnetism test, close inspection of grain size, and specific-gravity measurement can help distinguish basalt from andesite.