igneous
Basalt with Sulfide/Pyrite inclusion
Aphanitic Mafic Igneous Rock (likely Basalt) with Pyrite (FeS2)
Basalt: Fine-grained, dark grey to black, heavy, Mohs 5-6. Mineral inclusion: Metallic luster, brassy-yellow color, cubic or granular habit, Mohs 6-6.5.
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Physical properties
Basalt: Fine-grained, dark grey to black, heavy, Mohs 5-6. Mineral inclusion: Metallic luster, brassy-yellow color, cubic or granular habit, Mohs 6-6.5.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. The metallic inclusion likely formed through hydrothermal deposition or magmatic segregation.
Uses & applications
Basalt is used globally for construction aggregate, road base, and railroad ballast. The pyrite inclusions are generally of interest to collectors rather than industrial miners.
Geological facts
Basalt reflects the most common rock type in the Earth's crust, making up most of the ocean floor. Pyrite is often called 'Fool's Gold' because its color and luster can trick novice prospectors.
Field identification & locations
Identify in the field by its dark, fine-grained texture and heavy weight. The metallic patch will leave a greenish-black streak if tested. Commonly found in volcanic regions.
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