Ultramafic rock but there are ultrapotassic and highly silica-under-saturated rocks with >18% MgO which can be considered "ultramafic". Ultrapotassic, ultramafic igneous rocks such as lamprophyre, lamproite and kimberlite are known to have reached the surface of the Earth. Although no modern eruptions have been observed, analogues are preserved. Most of these rocks occur as dikes, diatremes, lopoliths or laccoliths, and very rarely, intrusions. Most kimberlite and lamproite occurrences occur as volcanic and subvolcanic diatremes and maars; lavas are virtually unknown. Vents of Proterozoic lamproite (Argyle diamond mine), and Cenozoic lamproite (Gaussberg, Antarctica) are known, as are vents of Devonian lamprophyre (Scotland). Kimberlite
Gemstone File Gemstone File The Gemstone File is a conspiracy theory document attributed to Bruce Porter Roberts. In 1975, "A Skeleton Key to the Gemstone File" appeared and is generally attributed to Stephanie Caruana. The "Key" is purportedly a synopsis of Roberts' documents that presents a chronicle of interlocking conspiracies, including claims that world events since the 1950s were shaped by suppressed information, the names of supposed shooters of President John F. Kennedy, and suggested connections between a number of political assassinations which occurred within a relatively short time frame. Authors James McConnachie and Robin Tudge called it "the original mega-conspiracy theory."