igneous
Quartz-veined Basalt
Amygdaloidal or Porphyritic Basalt with Silicon Dioxide (SiO2) vein
Hardness: 6-7 (Mohs scale), Color: Dark grey/green matrix with white/tan vein, Luster: Dull/earthy matrix with vitreous vein, Structure: Fine-grained (Aphanitic), Cleavage: None (conchoidal fracture on vein), Specific Gravity: 2.7–3.0
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Dark grey/green matrix with white/tan vein, Luster: Dull/earthy matrix with vitreous vein, Structure: Fine-grained (Aphanitic), Cleavage: None (conchoidal fracture on vein), Specific Gravity: 2.7–3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. The white vein formed later via hydrothermal activity, where mineral-rich water filled a cooling crack and crystallized as quartz or calcite.
Uses & applications
Basalt is primarily used in construction as crushed stone for road base, concrete aggregate, and railroad ballast. This specific small specimen is primarily of interest for amateur geology collecting or educational purposes.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. The white vein acts as a 'geological clock', showing that the host rock experienced a secondary tectonic or thermal event after it solidified.
Field identification & locations
Identify by its dark, heavy, fine-grained mass and the distinct contrasting mineral line. Often found near tectonic plate boundaries or volcanic island chains. Collectors should look for sharp color contrast and well-defined vein boundaries.
