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Picrite basalt is a variety of high magnesium olivine tholeiite basalt that is very rich in the mineral olivine. The rock type is also referred to as oceanite. It is dark with bright green olivine phenocrysts (20 to 50%) and black to dark brown pyroxene.
Picrite consists largely of olivine and titanium rich augite pyroxene with minor plagioclase and analcite set in a matrix of augite and more sodic plagioclase. It also may also contain chrysolite, hornblend and biotite.
The olivine rich picrite basalts that occur with the more common tholeiitic basalts of Kilauea and other volcanoes are likely the result of settling of olivine crystals either in a portion of the magma chamber or in a caldera lava lake.
Picrites and komatiites are similar chemically, but differ in that komatiite lavas exhibit the spinifex texture and have a higher magnesium content.
When the term oceanite was apparently first proposed by Lacroix, he used the term to apply only to basalts with more than 50% olivine content (an extremely rare occurrence). Picrite basalt is found in the lavas of Mauna Kea and Mauna Loa in Hawaii, Curaçao, in the Piton de la Fournaise volcano on Réunion Island and various other oceanic island volcanoes.
- Picrite basalt has been erupted in historical times from Mauna Loa during the eruptions of 1852 and 1868 (from different flanks of Mauna Loa).
- Picrite basalt with 30% olivine commonly erupts from the Piton de la Fournaise. *
Common Uses
Olivine basalt is a commonly used by foundries, boilermakers and boiler users to protect the area around a burner tip or to protect a floor from molten metal and other slag. Its use in this fashion is appropriate since olivine is a very refractory, high-melting temperature mineral.
References
- Carmichael, Ian S. E., Turner, Francis J., and Verhoogen, John; (1974) Igneous Petrology, McGraw-Hill, pp. 406 - 426.
- Metrich, Nicole, Françoise Pineau and Marc Javoy, 1988, Volatiles : Mantle Source Characterization and Degassing Process for Hot Spot Volcanism - The Piton de la Fournaise (Reunion Island) Example, http://www.the-conference.com/JConfAbs/1/88.html Retrieved 18 February 2006.
- Kerr, A. C. (1997) What is the difference between a komatiite and a picrite? http://www.le.ac.uk/geology/ack2/komatiite/difference.html retrieved 22 August 2005.
- Le Maitre, L.E., ed., (2002) Igneous Rocks: A Classification and Glossary of Terms 2nd edition, Cambridge.
- Rhodes, J. M., (1995) The 1852 and 1868 Mauna Loa Picrite Eruptions Geophysical Monograph Series, vol. 92, AGU, Abstract retrieved 18 February 2006.
- Wilkenson, J.F.G., and Hensel, H. D., 1988, The petrology of some picrites from Mauna Loa and Kilauea volcanoes, Hawaii: Contrib. Mineralogy and Petrology, v. 98, pp. 326-345.
- Williams, Howel, Francis J. Turner, and Charles M. Gilbert, 1954, Petrography W. H. Freeman, pp. 40 - 41.
"Picrite basalt"