Where is Epidote in Basalt found?
Epidote in Basalt
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Open the appEpidote in 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 Epidote in Basalt
Mid-ocean ridges and ophiolite complexes
These are prime locations for hydrothermally altered basalts, where seawater circulates through hot oceanic crust, leading to epidote formation. Examples include Cyprus, Oman, and various mountain ranges with obducted oceanic crust.
Subduction zones and volcanic arcs
Basalts in forearc and backarc basins, as well as volcanic islands, can undergo hydrothermal alteration and low-grade metamorphism, forming epidote. Examples include parts of the Pacific Ring of Fire.
Continental rift zones
Areas of continental rifting with associated basaltic volcanism can also exhibit epidote-bearing basalts due to geothermal activity. The East African Rift is an example.
Metamorphic terrains
Regions that have undergone regional low-grade metamorphism (greenschist facies) of basaltic protoliths will often contain epidote. Many ancient shield areas and orogenic belts globally.
Collecting tips
- Look for greenish hues. Epidote's characteristic pistachio-green color is a key indicator. Look for this color within the darker basalt matrix, especially in amygdules or veins.
- Examine altered zones. Focus on areas where basalt appears altered, such as near fault zones, hydrothermal vents (ancient or active), or areas with evidence of fluid flow.
- Check for amygdules. Vesicular basalts often have their gas bubbles (amygdules) filled with secondary minerals. Epidote is a common filling, sometimes alongside quartz, calcite, or zeolites.
- Consider the geological context. Understanding the regional geology and looking for areas known for hydrothermal alteration or low-grade metamorphism of basaltic rocks will increase your chances of finding epidote in basalt.
Quick Check
- Color:
- Pistachio-green to yellowish-green (epidote) within a dark, often greenish-tinged matrix (basalt).
- Luster:
- Vitreous to resinous (epidote), dull to sub-vitreous (basalt).
- Streak:
- White to grayish-white (epidote).
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