harzburgites

Harzburgite is an ultramafic rock of the Earth's mantle and a type of peridotite. It is considered a refractory residue produced by partial melting of fertile mantle rocks and is characterized by a dominant olivine–orthopyroxene assemblage with only minor to trace clinopyroxene.

Its mineralogy typically consists of olivine (often Fo-rich) and orthopyroxene, with clinopyroxene forming only a small fraction of the rock. Accessory minerals such as chromian spinel or garnet may be present, and textures are usually coarse-grained and granular, reflecting slow cooling in the mantle. The lack of substantial clinopyroxene distinguishes harzburgite from lherzolite, and its contrast with dunite is that dunite is dominated by olivine with very little pyroxene.

Harzburgite forms through partial melting of fertile peridotite, producing a rock depleted in basaltic components but enriched in olivine and orthopyroxene. It can occur as mantle residues beneath mid-ocean ridges and in subduction-zone mantle sections, and is a common component of ophiolites and mantle xenoliths carried to the surface by magmas.

Geochemically, harzburgites are important for studying the composition and evolution of the upper mantle and the processes of melt extraction. Their mineral and trace-element signatures help constrain mantle depletion trends and the nature of melt sources beneath different tectonic settings.