igneous
Basalt with Quartz/Feldspar Vein
Mafic Volcanic Rock (Basalt) with SiO2 hydrothermal vein
Hardness (6-7), Color (dark gray to black host rock with orange/tan vein), Luster (dull/earthy for host, vitreous for vein), Crystal structure (microcrystalline/aphanitic), Cleavage (none), Specific gravity (2.8-3.0)
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Physical properties
Hardness (6-7), Color (dark gray to black host rock with orange/tan vein), Luster (dull/earthy for host, vitreous for vein), Crystal structure (microcrystalline/aphanitic), Cleavage (none), Specific gravity (2.8-3.0)
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava. The vein formed later through hydrothermal activity where mineral-rich water filled a fracture in the rock and crystallized. Often Cenozoic to Precambrian in age depending on location.
Uses & applications
Basalt is primarily used as an aggregate in construction (roads, concrete), while similar river-smoothed specimens are used for decorative landscaping and decorative stone collecting.
Geological facts
The distinct line is called a 'xenolith' or more accurately a hydrothermal vein. These 'wishing stones' (rocks with a continuous white or colored ring/line) are popular charms in folklore.
Field identification & locations
Identify in the field by its heavy weight (high density), fine grain, and the distinct protrusion of the vein if the host rock is softer. Commonly found on beaches, rivers, and volcanic plateaus.
