Where is Peridotite found?
Peridotite (olivine-rich ultramafic rock)
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Open the appPeridotite 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 Peridotite
Ophiolite Complexes Worldwide
Examples include the Troodos Ophiolite (Cyprus), Semail Ophiolite (Oman), Coast Range Ophiolite (California, USA), and the Bay of Islands Ophiolite (Newfoundland, Canada). These represent fragments of oceanic lithosphere, including mantle peridotite, obducted onto continental margins.
Kimberlite Pipes
Found as xenoliths (mantle fragments) in kimberlite pipes, particularly in cratonic regions such as South Africa, Siberia, and Canada. These xenoliths provide direct samples of the Earth's deep mantle.
Layered Mafic Intrusions
Occurs as cumulate layers in large layered intrusions like the Bushveld Complex (South Africa), Stillwater Complex (Montana, USA), and Skaergaard Intrusion (Greenland). These are formed by fractional crystallization of mafic magmas.
Alpine-type Peridotites
Associated with orogenic belts, often highly serpentinized, such as in the Alps, Appalachians, and Urals. These are typically tectonically emplaced mantle rocks.
Collecting tips
- Look for Dark, Heavy Rocks. Peridotite is dense and typically dark green to black. Its high density can be a good initial indicator.
- Examine for Olivine Grains. Look for granular, often glassy-looking, yellowish-green to dark green crystals of olivine. A hand lens will be very useful.
- Check for Serpentinization. Many peridotites are partially or completely altered to serpentinite, which will appear as a waxy, often slick, green to black rock. Look for relict olivine or pyroxene grains within the serpentine matrix.
- Consider Geological Context. Search in areas known for ophiolites, ancient cratons, or regions with known kimberlite or large mafic intrusions. Understanding the regional geology is key.
- Test Hardness. Olivine has a hardness of 6.5-7 on the Mohs scale, so it will scratch glass and steel. Pyroxenes are slightly softer (5-6).
Quick Check
- Color:
- Dark green to yellowish-green, black, brownish-black
- Luster:
- Vitreous to greasy (olivine), vitreous (pyroxene)
- Streak:
- White to colorless
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