igneous
Polished dark mafic stone, likely basalt or diabase
Basalt/diabase; chiefly plagioclase feldspar and pyroxene, with possible olivine or iron-titanium oxides
AI-generated identification · may be incorrectFine-grained, dark gray to black, with a dull to satin luster and pale needle-like mineral specks; typical hardness is about 5–6 Mohs, no visible cleavage, and specific gravity roughly 2.8–3.1. The rounded, smooth surface indicates natural abrasion or tumbling/polishing.
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Physical properties
Fine-grained, dark gray to black, with a dull to satin luster and pale needle-like mineral specks; typical hardness is about 5–6 Mohs, no visible cleavage, and specific gravity roughly 2.8–3.1. The rounded, smooth surface indicates natural abrasion or tumbling/polishing.
Formation & geological history
Basalt forms when mafic lava cools rapidly at or near Earth’s surface; diabase is its somewhat coarser-grained shallow intrusive equivalent. Such rocks range from Precambrian to modern and occur in volcanic regions and ancient dike provinces.
Uses & applications
Used as aggregate, roadstone, paving, riprap, monuments, and landscaping stone; polished pieces are inexpensive décor or worry stones rather than jewelry gemstones.
Geological facts
The pale streaks are likely exposed feldspar or pyroxene crystals, not necessarily fibers. A streak test on unglazed ceramic should be gray, and a magnet may respond weakly if magnetite is present.
Field identification & locations
Common worldwide, especially in volcanic belts and basalt plateaus; identify by its dense dark color, fine texture, lack of layering, and hardness. Exact identification requires a fresh surface or thin-section analysis.
