Where is Olivine Basalt found?
Basalt with Olivine phenocrysts
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Open the appOlivine Basalt occurs in specific geological environments. Knowing where to look, and in what kind of rock, is the difference between going home empty-handed and finding a great specimen.
Where to find Olivine Basalt
Mid-Ocean Ridges
The most extensive source, though often submerged. Samples can be obtained from ophiolite complexes where oceanic crust has been obducted onto continents.
Oceanic Islands
Volcanic islands formed over hotspots, such as Hawaii, Iceland, and the Galapagos, are rich in olivine basalt flows.
Continental Flood Basalt Provinces
Large igneous provinces like the Deccan Traps (India), Siberian Traps (Russia), and Columbia River Basalt Group (USA) contain vast quantities of olivine basalt.
Continental Rift Zones
Areas where continents are pulling apart, such as the East African Rift Valley, often feature olivine basalt volcanism.
Collecting tips
- Look for Dark, Fine-Grained Rocks. Basalts are typically dark. The fine-grained nature indicates rapid cooling.
- Identify Green Phenocrysts. The key diagnostic feature is the presence of visible, often glassy-looking, yellowish-green to green olivine crystals. Use a hand lens if necessary.
- Check for Vesicles. Many basalts are vesicular, containing small, rounded holes formed by gas bubbles. This is a common feature but not exclusive to olivine basalt.
- Consider the Geological Context. If you are in a volcanic region, especially one associated with oceanic crust or rift zones, the likelihood of finding olivine basalt increases.
Quick Check
- Color:
- Dark gray to black with green spots
- Luster:
- Dull to earthy (groundmass), vitreous to greasy (olivine)
- Streak:
- White to grayish-white (difficult to obtain due to hardness)
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