igneous
Polished basalt with chalcedony/agate vein
Basalt (fine-grained mafic volcanic rock) with microcrystalline quartz, SiO₂
AI-generated identification · may be incorrectDark gray-black, fine-grained and granular with a glossy polish; the translucent brown-gray band is likely chalcedony or agate. Basalt hardness is about 6–7 Mohs, quartz-rich vein about 7; no obvious cleavage, with generally high specific gravity around 2.8–3.1.
Identified More igneous →
Explore Polished basalt with chalcedony/agate vein in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray-black, fine-grained and granular with a glossy polish; the translucent brown-gray band is likely chalcedony or agate. Basalt hardness is about 6–7 Mohs, quartz-rich vein about 7; no obvious cleavage, with generally high specific gravity around 2.8–3.1.
Formation & geological history
Basalt formed from rapidly cooled mafic lava, commonly in volcanic flows, while silica-rich fluids later filled a cavity or fracture to produce chalcedony/agate. The specimen’s exact geological age and locality cannot be determined from the image.
Uses & applications
Used mainly as a decorative, polished, or lapidary specimen; basalt is also used for aggregate, paving, and construction stone. The vein adds modest ornamental and collecting interest.
Geological facts
The granular dark matrix may also be a related mafic volcanic rock such as diabase, but the image favors basalt. Translucent chalcedony commonly displays waxy luster and curved internal banding.
Field identification & locations
Identify it by its heavy dark matrix, tiny interlocking crystals, and contrasting translucent quartz vein; a glassy streak or bubbles would suggest artificial glass instead. Common settings include volcanic provinces worldwide, especially flood-basalt regions and ancient lava flows.
