English: Kimberlite from the Jurassic of Pennsylvania, USA. (~4.6 cm across at its widest)

Kimberlites and lamproites have tremendous economic importance because they are host rocks for gem-grade and industrial-grade diamonds. Kimberlites & lamproites are unusual igneous bodies having overall pipe-shaped geometries. Their mode of formation is only moderately understood because they have not been observed forming. Kimberlites & lamproites are known from scattered localities throughout the world - only some are significantly diamondiferous. Classic localities for diamonds are India and Brazil. Africa was also discovered to have many kimberlites and is world-famous for producing large numbers of diamonds. Other notable diamondiferous kimberlite-lamproite occurrences include Russia, China, northwestern Australia, and northwestern Canada.

Kimberlites are named for the town of Kimberley, South Africa. Several kimberlite pipes occur in the Kimberley area. Kimberlites have a gently tapering-downward, pipe-shaped cross-section. Lamproites have a cross-section more closely resembling that of a martini glass.

The rock shown above is from a non-diamondiferous kimberlite intrusion in Pennsylvania. Unlike most kimberlites, which have pipe-shaped geometries, this occurrence is an igneous dike. The groundmass consist of olivine, phlogopite mica, and opaque minerals. Phenocrysts and megacrysts reported from this unit include olivine (serpentinized) and pyrope garnet.

Geologic unit: Gates-Adah Kimberlite Dike, middle Early Jurassic, 185 Ma

Locality: Gates-Adah Kimberlite Dike trend, near Middle Run, east of the Monongahela River, north or northeast of the town of Gates, far-western Fayette County, southwestern Pennsylvania, USA