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 Originally distributed in 1975 by hand and mail in photocopy form, the Gemstone File has appeared in slightly revised form in Hustler magazine and on the Internet. Roberts, known only to Stephanie Caruana and conspiracy theorist Mae Brussell, purportedly began gathering information in the file when Howard Hughes stole his invention for processing synthetic rubies, hence the title "Gemstone". According to Gerald Carroll, Roberts was born in New York State on October 27, 1919 and died of lung cancer in San Francisco on July 16, 1976. "Factsheet Five" publisher Mike Gunderloy collected and distributed several versions of the Gemstone File.