igneous
Polished black stone, likely basalt or dark river pebble
Basalt; chiefly plagioclase feldspar and pyroxene, commonly with minor magnetite
AI-generated identification · may be incorrectDark gray to black, smooth and rounded from tumbling or water abrasion, with a dull to faintly vitreous luster. Basalt has Mohs hardness about 6, no visible cleavage in fine-grained pieces, and specific gravity around 2.8–3.0; the image alone cannot confirm the identification.
Identified More igneous →
Explore Polished black stone, likely basalt or dark river pebble in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray to black, smooth and rounded from tumbling or water abrasion, with a dull to faintly vitreous luster. Basalt has Mohs hardness about 6, no visible cleavage in fine-grained pieces, and specific gravity around 2.8–3.0; the image alone cannot confirm the identification.
Formation & geological history
Basalt forms when low-silica lava cools rapidly at or near Earth’s surface, commonly in volcanic fields and oceanic crust. Its age may range from recent eruptions to billions of years.
Uses & applications
Used as aggregate, road stone, riprap, paving, and occasionally as a polished decorative or meditation stone; ordinary pieces have little jewelry value.
Geological facts
The specimen’s rounded shape and polish obscure its original texture, so it could also be another dark rock such as slate, hornfels, or a manufactured glass-like material.
Field identification & locations
Look for a fine-grained texture, black streak or gray powder, lack of bubbles, and weak attraction to a magnet if magnetite is present; a streak, hardness, and density test would improve identification. Common sources include volcanic regions and river gravels.
