igneous
Olivine-rich Basalt with Peridotite Xenoliths
Porphyritic Basalt containing Dunite/Peridotite (Mg,Fe)2SiO4
Hardness: 6.5-7 (olivine) / 5-6 (matrix); Color: Dark gray to black matrix with olive-green inclusions; Luster: Vitreous to grainy; Crystal structure: Orthorhombic crystals in an aphanitic groundmass; Specific Gravity: 3.0-3.3
- Hardness
- 6
- Color
- Dark gray to black matrix with olive-green inclusions
- Luster
- Vitreous to grainy
Identified More igneous →
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Physical properties
Hardness: 6.5-7 (olivine) / 5-6 (matrix); Color: Dark gray to black matrix with olive-green inclusions; Luster: Vitreous to grainy; Crystal structure: Orthorhombic crystals in an aphanitic groundmass; Specific Gravity: 3.0-3.3
Formation & geological history
Formed through volcanic activity where basaltic magma carries fragments of the Earth's upper mantle (xenoliths) to the surface. These green nodules are peridotite, formed at high pressures and temperatures.
Uses & applications
Used in geological research to study the Earth's mantle, as decorative stones, or for extracting olivine (peridot) for jewelry if crystals are large and clear enough.
Geological facts
The green nodules are essentially 'alien' rocks from the deep earth that did not melt into the magma. Large versions of these are found at San Carlos, Arizona, and in volcanic fields in Hawaii and the Canary Islands.
Field identification & locations
Identify by looking for distinct green, glassy 'grains' or 'nodules' embedded in a dark, fine-grained volcanic rock. Often found in recent volcanic flows or as weathered river cobbles in volcanic regions.
