igneous
Peridotite Nodules in Basalt (Olivine Xenolith)
Mantle Peridotite / Olivine ((Mg, Fe)2SiO4) in Basalt
Hardness: 6.5-7.0 for olivine. Color: Yellowish-green to olive green (olivine) embedded in dark gray to black fine-grained basalt matrix. Luster: Vitreous to dull. Crystal Structure: Orthorhombic granular crystals inside microcrystalline mafic rock. Specific Gravity: ~3.2-3.4.
- Hardness
- 6
- Luster
- Vitreous to dull
Identified More igneous →
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Physical properties
Hardness: 6.5-7.0 for olivine. Color: Yellowish-green to olive green (olivine) embedded in dark gray to black fine-grained basalt matrix. Luster: Vitreous to dull. Crystal Structure: Orthorhombic granular crystals inside microcrystalline mafic rock. Specific Gravity: ~3.2-3.4.
Formation & geological history
Formed deep within the Earth's upper mantle at high pressures and temperatures. Mantle fragments (xenoliths) are brought to the surface quickly by fast-ascending basaltic magma during volcanic eruptions. Found in volcanic terrain globally, such as Hawaii, Arizona, Germany (Eifel), and ocean islands.
Uses & applications
Used scientifically to study the earth's mantle composition. Gem-quality olivine (peridot) is cut into gemstones for jewelry. Raw nodules are popular among rock and mineral collectors.
Geological facts
Peridotite xenoliths are literal pieces of the Earth's mantle brought up from depths of 30 to over 100 kilometers below the surface. They offer geologists a direct look at the composition of the deep Earth.
Field identification & locations
Identified by distinct light green or yellowish-green granular patches of olivine enclosed in a dark, fine-grained volcanic (basaltic) rock exterior, often smoothed by stream or beach erosion. Collect near volcanic fields or riverbeds in volcanic regions.
