Ultramafic rock

Rare occurrences may include unusual surface deposits of maars of kimberlites in the diamond fields of southern Africa and other regions.

Ultrapotassic, ultramafic igneous rocks such as lamprophyre, lamproite and kimberlite are known to have reached the surface of the Earth.

Most kimberlite and lamproite occurrences occur as volcanic and subvolcanic diatremes and maars; lavas are virtually unknown.

Kimberlite pipes in Canada, Russia and South Africa have incompletely preserved tephra and agglomerate facies.

These are generally diatreme events and as such are not lava flows although tephra and ash deposits are partially preserved.

When such metamorphic fluids have less than 10% molar proportion of CO2, reactions favor serpentinisation, resulting in chlorite-serpentine-amphibole type assemblages.

The majority of ultramafic rocks are exposed in orogenic belts, and predominate in Archaean and Proterozoic terranes.

Often thick, magnesite-calcrete caprock, laterite and duricrust forms over ultramafic rocks in tropical and subtropical environments.

Particular floral assemblages associated with highly nickeliferous ultramafic rocks are indicative tools for mineral exploration.

The magma immediately below these hot spots is probably about 200 °C (360 °F) hotter, based on surface-to-subsurface temperature differences observed for lava on Earth.