igneous
Basalt with Quartz Veins
Aphanitic Mafic Igneous Rock (primarily Plagioclase and Pyroxene) with SiO2 inclusions
Hardness: 5-6 (Basalt), 7 (Quartz); Color: Dark grey to black matrix with white or orange-stained veins; Luster: Dull/Earthy; Structure: Fine-grained; Cleavage: None
- Hardness
- 5-6 (Basalt), 7 (Quartz)
- Color
- Dark grey to black matrix with white or orange-stained veins
- Luster
- Dull/Earthy
Identified More igneous →
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Physical properties
Hardness: 5-6 (Basalt), 7 (Quartz); Color: Dark grey to black matrix with white or orange-stained veins; Luster: Dull/Earthy; Structure: Fine-grained; Cleavage: None
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the Earth's surface. The veins formed later when hydrothermal fluids filled cooling cracks, precipitating quartz and iron oxides.
Uses & applications
Commonly used as crushed stone in construction, road base, and railroad ballast. This specific small, water-worn beach pebble is primarily for coastal collecting.
Geological facts
Basalt is the most common rock type in the Earth's crust and covers most of the ocean floor. The orange tint in the veins of this specimen is likely due to iron oxide staining (rusting) of the quartz minerals.
Field identification & locations
Found frequently on beaches in volcanic regions (like the Pacific Northwest or Iceland). Identified by its dark, heavy, fine-grained mass and contrasting light-colored mineral veins.
