metamorphic
Eclogite
Eclogite (Omphacite + Pyrope-Almandine Garnet)
Hardness of 6.5-7.5 on the Mohs scale, distinct dark green (omphacite) and reddish-pink to deep red (pyrope garnet) colors, submetallic to vitreous luster, massive or granular crystal structure, poor cleavage, and a relatively high specific gravity (3.4-3.8 g/cm³).
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Physical properties
Hardness of 6.5-7.5 on the Mohs scale, distinct dark green (omphacite) and reddish-pink to deep red (pyrope garnet) colors, submetallic to vitreous luster, massive or granular crystal structure, poor cleavage, and a relatively high specific gravity (3.4-3.8 g/cm³).
Formation & geological history
Formed through ultra-high-pressure (UHP) metamorphism of basalt or gabbro deep within the Earth's mantle (at depths greater than 35-50 km), typically brought back to the surface via subduction zone tectonics.
Uses & applications
Primarily used for scientific research to understand deep Earth dynamics, mantle petrology, and plate tectonics. Rarely used as a lapidary stone when it features attractive contrasting garnet and pyroxene.
Geological facts
Eclogite is a relatively rare and remarkable rock because its presence at the Earth's surface proves that rocks from the deep crust and upper mantle can be subducted and subsequently exhumed.
Field identification & locations
Identified in the field by its striking red and green mottled appearance. Commonly found in major metamorphic mountain belts and ophiolite complexes associated with ancient subduction zones, such as the Franciscan Complex in California or parts of Norway.
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