Kimberlite pipes are windows into the upper mantle, and the various xenoliths that have been recovered from the pipes have provided new data for the construction of a structural model for the upper mantle under the continents.

Diamond-bearing eclogite and garnetiferous ultramafic inclusions are of critical importance, as the mineral and rock inclusions contained in the diamonds provide data on the mineral assemblages and phases that were in equilibrium with the diamonds at the time of crystallization.

The chemistry of the mineral phases associated with the diamonds indicates that crystallization occurred under conditions of low oxygen potential and that the appearance of free carbon as graphite or diamond is encouraged by decreasing oxygen potential.

The lack of biotite (phlogopite) inclusions in diamond indicates that biotite probably crystallizes at higher levels in the upper mantle, where potassium enrichment has occurred.