Basanite

This article is about the igneous rock, basanite is also a variety of jasper

Basanite

[[|Igneous rock]]

Volcanic bomb of black basanite enclosing a xenolith of green dunite from Réunion

File:Montemartini - Agrippina minore 1030446.JPG

Basanite statue of Agrippina Minor

Basanite /ˈbæsənaɪt/ is an igneous, volcanic (extrusive) rock with aphanitic to porphyritic texture.

The mineral assembly is usually abundant feldspathoids (nepheline or leucite), plagioclase, and augite, together with olivine and lesser iron-titanium oxides such as ilmenite and magnetite-ulvospinel; minor alkali feldspar may be present, as illustrated by the position of the field for basanite in the QAPF diagram. Clinopyroxene (augite) and olivine are common as phenocrysts and in the matrix. The augite contains significantly greater titanium, aluminium and sodium than that in typical tholeiitic basalt. Quartz is absent, as are orthopyroxene and pigeonite. Chemically, basanites are low in silica (42 to 45% SiO₂) and high in alkalis (3 to 5.5% Na₂O and K₂O) compared to basalt, which typically contains more SiO₂, as evident on the diagram used for TAS classification. Nephelinite is yet richer in Na₂O plus K₂O compared to SiO₂.

Basanites occur both on continents and on ocean islands. For example, together with basalts, they are produced by hotspot volcanism in the Hawaiian and the Comoros Islands.

References

• Blatt, Harvey and Robert J. Tracy (1996) Petrology, 2nd ed., W. H. Freeman ISBN 0-7167-2438-3
• Buchwaldt, Robert (2003) Geochemistry and Petrology of a Miocene Trachyte-Basanite Suite from Mt. Tsaratanana, Northern Madagascar, Abstract.