Where is Olivine Basalt found?
Basalt (mafic volcanic rock) with Olivine (Mg,Fe)2SiO4
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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
Hawaii, USA
Extensive occurrences on all Hawaiian islands, particularly Kilauea and Mauna Loa, where olivine-rich basalts are common in lava flows.
Iceland
Widespread across the island, a result of its location on the Mid-Atlantic Ridge and a mantle plume.
Columbia River Basalt Group, USA
Large igneous province in the Pacific Northwest, though olivine phenocrysts are less ubiquitous than in oceanic basalts, they are present in some flows.
Deccan Traps, India
One of the largest flood basalt provinces globally, containing various basaltic compositions, including olivine-bearing types.
Mid-ocean ridges worldwide
Commonly found in samples dredged from mid-ocean ridge systems, representing newly formed oceanic crust.
Collecting tips
- Look for dark, fine-grained rocks. Basalt is typically dark gray to black. The presence of visible green crystals is the key indicator for olivine phenocrysts.
- Examine fresh surfaces. Weathering can alter the color of olivine to reddish-brown (iddingsite) or obscure its characteristic green hue. Look for freshly broken surfaces.
- Check for vesicularity. Many basalts are vesicular (contain gas bubbles), which can be a helpful textural clue, though not diagnostic of olivine presence.
- Consider the geological context. Basalts are associated with volcanic activity. Look in areas with lava flows, volcanic cones, or dikes/sills cutting through other rocks.
Quick Check
- Color:
- Dark gray to black groundmass with green to yellowish-green phenocrysts.
- Luster:
- Dull to sub-vitreous groundmass, vitreous phenocrysts.
- Streak:
- White to grayish-white (for the bulk rock, though individual olivine streak is white).
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