metamorphic

Polished black-and-brown river pebble

Likely altered basalt or hornfels; exact identification requires testing

AI-generated identification · may be incorrect

Dark brown-black, fine-grained, opaque, and strongly polished with a glassy-to-waxy luster; likely hardness about 5.5–7 Mohs, with no visible cleavage or crystals. The rusty-brown areas may reflect iron-oxide staining or weathered minerals.

Identified September 11, 2026More metamorphic →

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Physical properties

Formation & geological history

Probably a naturally rounded, water-worn stone later tumbled or polished; if basaltic, it formed from volcanic lava, while hornfels formed by contact metamorphism. Geological age cannot be determined from the photograph.

Uses & applications

Used as a decorative pebble, worry stone, craft material, or landscaping stone; it has little jewelry value unless confirmed as a desirable jasper, obsidian, or other lapidary material.

Geological facts

The elongated form and smooth surface indicate abrasion by water or mechanical tumbling. Surface reflections and mottled coloring are insufficient to distinguish basalt, jasper, hornfels, or slag confidently.

Field identification & locations

Check streak, hardness, magnetism, and texture: a fine-grained natural stone should lack bubbles and show an earthy gray-black streak; abundant vesicles or glassy flow texture suggest basalt or obsidian, while bubbles could indicate slag. Common analogous pebbles occur in volcanic or metamorphic river gravels.