Kimberlite and of those just over 30 have been economic enough to diamond mine. The deposits occurring at Kimberley, South Africa, were the first recognized and the source of the name. The Kimberley diamonds were originally found in weathered kimberlite, which was colored yellow by limonite, and so was called "yellow ground". Deeper workings encountered less altered rock, serpentinized kimberlite, which miners call "blue ground". See also Mir Mine and Udachnaya pipe, both in the Sakha Republic, Siberia. The blue and yellow ground were both prolific producers of diamonds. After the yellow ground had been exhausted, miners in the late 19th
Volcanic rock that after the mineral had crystallized it was partly again dissolved or corroded at some period before the matrix solidified. Corroded phenocrysts of biotite and hornblende are very common in some lavas; they are surrounded by black rims of magnetite mixed with pale green augite. The hornblende or biotite substance has proved unstable at a certain stage of consolidation, and has been replaced by a paramorph of augite and magnetite, which may partially or completely substitute for the original crystal but still retains its characteristic outlines. Volcanic rock Volcanic rock (often shortened to volcanics in scientific contexts) is a rock