What Diamond is to kimberlite and Lamproite

Diamond is....
... to Kimberlite & Lamproite

The complex volcanic magmas that solidify into kimberlite and lamproite are not the source of diamonds, only the elevators that bring them with other minerals and mantle rocks to Earth's surface.

Although rising from much greater depths than other magmas, these pipes and volcanic cones are relatively small and rare, but they erupt in extraordinary supersonic explosions.

Kimberlite and lamproite are similar mixtures of rock material. Their important constituents include fragments of rock from Earth's mantle, large crystals, and the crystallized magma that glues the mixture together.

The magmas are very rich in magnesium and volatile compounds such as water and carbon dioxide. As the volatiles dissolved in the magma change to gas near Earth's surface, explosive eruptions create the characteristic carrot- or bowl-shaped pipes.

Kimberlite magma rises through Earth's crust in networks of cracks or dikes. The pipes only form near Earth's surface. This cross-section of a kimberlite pipe shows the carrot-shaped profile produced by explosive eruption.

The root zone starts in fissures, where gases are released from the rising magma and drive the eruption; they blow out the fragment-laden kimberlite to form the volcano's tuff ring and fill the pipe. Depth measurements show the level of erosion for various kimberlite pipes in South Africa. Adapted from Hawthorne (1975).

These drawings illustrate the formation and filling of the typical champagne-glass shape of a lamproite pipe.

The initial stage of the eruption, powered by gases either from the lamproite magma or from boiling ground water, corrodes the hosting rock to form the champagne-glass shape (top).

The eruption then produces particles of ash, lapilli, and pumice that partially fill the crater and form a tuff ring (middle).

Finally, the crater fills with a lava pond from the degassed lamproite magma (bottom).

Adapted from a sketch by Barbara Scott-Smith..