Eclogite

Physical Properties

Hardness: 6.5–7.5 (Mohs); Color: Mottled red and green (this specimen appears weathered/oxidized); Luster: Vitreous to dull; Crystal Structure: Granular/Granoblastic; Specific Gravity: 3.2–3.6.

Formation & Geological History

Formed under extremely high pressure and high temperature conditions (HP/HT metamorphic facies) in subduction zones, typically from mafic igneous rocks (basalt or gabbro) being pushed deep into the Earth's mantle.

Uses & Applications

Primarily of scientific interest for studying mantle dynamics; occasionally used as a heavy-duty aggregate or as a semi-precious decorative stone if garnet content is high and colorful.

Geological Facts

Eclogite is often called the 'Christmas Tree Rock' because of its classic bright green (omphacite pyroxene) and red (almandine-pyrope garnet) coloring. It is an indicator of the deepest levels of mountain-building processes.

Field Identification & Locations

Identify by its unusually high density (heavy for its size) and the presence of small, rounded garnets embedded in a pyroxene matrix. Commonly found in orogenic belts like the Alps or the Norwegian Caledonides.

Identified on: 4/30/2026

Mode: Standard