metamorphic
Eclogite
Eclogite (composed primarily of Omphacite and Pyrope Garnet)
Hardness: 6.5-7.5 (Mohs scale); Color: green matrix (omphacite) with red to pink spots (garnet); Luster: vitreous to dull; Crystal structure: granular/monoclinic/isometric; Specific gravity: 3.2-3.6 (very dense).
- Hardness
- 6
- Color
- green matrix (omphacite) with red to pink spots (garnet)
- Luster
- vitreous to dull
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Physical properties
Hardness: 6.5-7.5 (Mohs scale); Color: green matrix (omphacite) with red to pink spots (garnet); Luster: vitreous to dull; Crystal structure: granular/monoclinic/isometric; Specific gravity: 3.2-3.6 (very dense).
Formation & geological history
Formed at extremely high pressures and relatively high temperatures in the earth's mantle or deep crustal levels during subduction of oceanic crust. Specimens are often millions of years old, typically reaching the surface through tectonic uplift.
Uses & applications
Primarily used as a decorative stone, in jewelry (the garnets), and as a valuable geological indicator of tectonic processes. Some industrial use as an abrasive due to high hardness.
Geological facts
Eclogite is often called the 'Christmas Rock' because of its striking green and red coloration. It provides some of the best evidence we have for the chemical composition of the deep upper mantle.
Field identification & locations
Identify by its unusually high density (it feels heavy for its size) and the distinct 'salt and pepper' or 'mottled' texture of green pyroxene and red garnet. Commonly found in mountain belts where deep crustal rocks have been uplifted, such as the Alps or the Norwegian Caledonides.
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