Pyrolite

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Pyrolite is a theoretical rock considered to be the best approximation of the composition of Earth's upper mantle. The definition varies, but it is generally considered as being 1 part tholeiitic basalt and 3 parts peridotite (specifically, harzburgite). If fused experimentally, this mix yields high pressure tholeiitic basaltic melts, and intermediate pressure alkaline basalts.