The formation conditions of garnet

Garnet also has its function in the analysis of rock metamorphism. Eclogite, for example, can be defined as a rock with a basalt composition, but mainly composed of garnet and omphacite. Garnet containing more garnet components can only be produced in relatively high pressure metamorphic rocks, such as the bottom of the Earth's crust and rocks in the mantle. Peridotite may contain Plagioclase, aluminum-rich spinel, or garnet rich garnet, and the presence of all three minerals at the same time confirms a pressure temperature zone in which the Peridot and pyroxene minerals balance. The above three minerals are arranged according to their stability in the peridotite mineral collection under increased pressure. So garnet peridotite can only be formed deep in the earth's crust. The Xenolith of garnet peridotite is brought up from a depth of 100km or more by kimberlite, and the garnet contained in the xenolith fragments is used as an indicator mineral for kimberlite in diamond prospecting. At depths of 300 to 400km and beyond, the pyroxene components dissolve into the garnet as (Mg,Fe) and Si replace the 2Al in the regular octahedral (Y) position of the garnet, creating a garnet with an unusually high silicon content and solid solution properties as a magnesia ferric garnet. This high silicon content of garnet was confirmed to be contained in diamonds.