igneous
Magnetite-rich Basalt
Basalt containing Fe3O4
Hardness: 5.5-6.5 (Mohs scale); Color: Dark grey to black with metallic flecks; Luster: Sub-metallic to dull; Crystal structure: Fine-grained aphanitic with occasional phenocrysts; Specific gravity: Approx 3.0-5.2 depending on iron content.
- Hardness
- 5
- Color
- Dark grey to black with metallic flecks
- Luster
- Sub-metallic to dull
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Physical properties
Hardness: 5.5-6.5 (Mohs scale); Color: Dark grey to black with metallic flecks; Luster: Sub-metallic to dull; Crystal structure: Fine-grained aphanitic with occasional phenocrysts; Specific gravity: Approx 3.0-5.2 depending on iron content.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. The presence of magnetite suggests a high iron concentration during crystallization. Found in volcanic provinces and oceanic crust.
Uses & applications
Primary source of iron ore (the magnetite component), used as crushed stone in construction, road base, and as a concrete aggregate. Small specimens are popular for teaching magnetism.
Geological facts
Magnetite is the most magnetic of all the naturally-occurring minerals on Earth. When basaltic lava cools, these minerals align with Earth's magnetic field, allowing geologists to study paleomagnetism and continental drift.
Field identification & locations
Identify in the field by its high density, dark color, and strong reaction to a hand magnet. It will often produce a black streak on a porcelain plate. Common in areas with historical volcanic activity.
