igneous
Polished basalt with a quartz vein
Basalt, cut by milky quartz (SiO₂)
AI-generated identification · may be incorrectFine-grained, dark gray to black, dense, and typically nonvesicular; the white band is massive quartz with vitreous to waxy luster. Basalt hardness is about 6, while quartz is 7; cleavage is absent or poor, and specific gravity is roughly 2.8–3.0.
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Physical properties
Fine-grained, dark gray to black, dense, and typically nonvesicular; the white band is massive quartz with vitreous to waxy luster. Basalt hardness is about 6, while quartz is 7; cleavage is absent or poor, and specific gravity is roughly 2.8–3.0.
Formation & geological history
Basalt formed from rapidly cooled mafic lava, commonly during volcanic eruptions, while the quartz vein crystallized later from silica-rich hydrothermal fluids filling a fracture. The specimen’s precise geological age and locality cannot be determined from the photograph.
Uses & applications
Used as a polished ornamental stone, paperweight, or teaching specimen; basalt is widely used for aggregate, roadstone, and construction, while quartz is valued for glass, electronics, and mineral collecting.
Geological facts
The sharp, contrasting white vein records secondary mineralization after the host rock formed. Dark basalt may also contain plagioclase, pyroxene, and minor olivine or iron oxides.
Field identification & locations
Identify it by its dark fine-grained host, high density, and bright white quartz cross-cutting vein; a streak, hardness, and magnification test can confirm it. Similar material occurs in volcanic regions worldwide, including Iceland, India, Hawaii, and the Pacific Northwest.
