igneous
Olivine Basalt (with Epidote and Serpentine)
Mafic Volcanic Rock (Basalt)
Hardness around 5.5 to 6.5 on Mohs scale. Colors range from dark grey, brownish black, to yellowish-green hues due to olivine/epidote content. Dull to earthy luster, fine-grained (aphanitic) texture with microcrystalline matrix.
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Physical properties
Hardness around 5.5 to 6.5 on Mohs scale. Colors range from dark grey, brownish black, to yellowish-green hues due to olivine/epidote content. Dull to earthy luster, fine-grained (aphanitic) texture with microcrystalline matrix.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. Secondary alteration processes, such as hydrothermal fluids, often introduce green secondary minerals like epidote or serpentine into cavities and fractures.
Uses & applications
Basalt is widely used in construction as crushed stone for concrete aggregate, road base, and railroad ballast. Unaltered green olivine crystals can be used as gemstones (peridot).
Geological facts
Basalt is the most common rock type in the Earth's crust, making up most of the oceanic crust. Olivine-bearing basalt is also found extensively on the Moon and Mars.
Field identification & locations
Identify in the field by its dark color, heavy weight relative to size, fine grain, and distinct yellowish-green to olive-green patches or coatings. Commonly found in volcanic regions, oceanic island chains, and rift valleys.
