metamorphic
Eclogite garnet in matrix
Eclogite (Garnet-Omphacite rock)
Hardness: 6.5-7.5 (garnet) and 5-6 (omphacite); Color: Red or pink garnets in a light-green or gray-white matrix; Luster: Vitreous to dull; Crystal structure: Isometric (garnet) and Monoclinic (pyroxene); High specific gravity (~3.4–3.5).
- Hardness
- 6
- Color
- Red or pink garnets in a light-green or gray-white matrix
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6.5-7.5 (garnet) and 5-6 (omphacite); Color: Red or pink garnets in a light-green or gray-white matrix; Luster: Vitreous to dull; Crystal structure: Isometric (garnet) and Monoclinic (pyroxene); High specific gravity (~3.4–3.5).
Formation & geological history
Formed at extremely high pressures (over 1.2 GPa) and moderate to high temperatures in subduction zones, often representing metamorphosed oceanic crust (basalt or gabbro) dragged deep into the Earth's mantle.
Uses & applications
Primarily used as a 'messenger from the deep' for geological research on plate tectonics; occasionally used as an abrasive or as a decorative gemstone 'ruby-in-matrix' (though eclogite contains garnets, not rubies).
Geological facts
Eclogite is often called the 'Christmas Tree Rock' because of its classic red garnet and green omphacite coloring. It is one of the densest silicate rocks in the Earth's crust.
Field identification & locations
Identify by looking for deep red, rounded garnet 'eyes' (porphyroblasts) embedded in a dense, usually green or pale matrix. Its high weight for its small size is a key identifying factor. Found in orogenic belts like the Alps or the coast of Norway.
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